UNIVERSITY  OF   CALIFORNIA 

COLLEGE    OF    AGRICULTURE 

AGRICULTURAL    EXPERIMENT    STATION 

BERKELEY,    CALIFORNIA 


THE  PRINCIPLES  AND  PRACTICE 
OF  SUN-DRYING  FRUIT 


BY 
A.  W.  CHRISTIE  AND  L.  C.  BARNARD 


BULLETIN  No.  388 

May,  1925 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1925 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/principlespracti388chri 


THE  PRINCIPLES  AND  PRACTICE  OF 
SUN-DRYING  FRUIT 

By  A.  W.  CHRISTIE  and  L.  C.  BARNARD 


EXTENT  OP  THE  DRIED  FRUIT  INDUSTRY 

From  the  beginning  of  fruit  growing  in  California,  sun-drying 
has  been  one  of  the  principal  methods  of  preserving  fruit  for  market- 
ing. While  sometimes  used  as  a  means  of  preserving  fruit  which  could 
not  be  marketed  through  other  channels  such  as  fresh  sale  or  canning, 
sun-drying  is  a  primary  industry,  as  evidenced  by  the  large  proportion 
of  fruits  grown  expressly  for  drying.  The  quality  and  world-wide 
distribution  of  her  dried  fruits  have  made  California  the  leader  of 
the  world  in  this  field.  In  fact,  the  dried  fruits  of  California  are 
considered  the  standard  of  excellence. 

Various  causes  have  contributed  to  the  development  of  sun-drying 
in  California,  the  most  important  being  its  sub-tropical  climate.  The 
long,  warm,  dry  summer  is  not  only  favorable  to  the  production  of  the 
principal  drying  fruits,  but  since  the  ripening  of  most  of  these  fruits 
normally  occurs  in  dry  weather,  it  is  possible  to  utilize  this  simple, 
natural  method  of  food  preservation.  Because  California  is  situated 
several  thousands  miles  from  her  principal  markets,  dried  fruits  repre- 
sent the  most  economical  form  in  which  the  crops  can  be  transported 
and  offered  for  sale.  Although  cooperative  canneries  are  growing, 
drying  is  in  general  the  principal  method  by  which  the  individual 
grower  can  preserve  his  crop  in  a  durable  form.  The  great  increase 
in  the  production  of  dried  fruits  in  recent  years  has  been  largely  due 
to  the  activities  of  the  several  cooperative  marketing  associations. 
These  associations  have  enabled  the  growers  to  retain  control  of  their 
dried  products  through  all  the  stages  of  packing  and  distribution  to 
the  ultimate  consumer  and  by  means  of  standardization,  attractive 
packaging  and  advertisement  to  very  greatly  increase  the  demand  for 
California  dried  fruits. 

According  to  the  1919  census,  California  produced  94  per  cent  of 
all  the  dried  fruits  of  the  United  States.  With  the  exception  of  prunes 
in  the  Pacific  Northwest  and  evaporated  apples  in  several  states,  Cali- 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

fornia  enjoys  a  practical  monopoly  in  the  production  of  nearly  all 
kinds  of  dried  fruits.  The  extent  of  the  industry  can  be  seen  by 
reference  to  Table  1,  which  gives  the  tonnage  produced  in  1923  with 
a  conservative  estimate  of  their  value  to  the  producer.  Table  2, 
gives  the  total  acreages  of  certain  fruits  for  1924.  It  is  difficult  to 
estimate  what  proportion  of  these  acreages  were  devoted  to  the  pro- 
duction of  dried  fruits.  In  most  cases,  the  proportion  of  the  total 
crop  which  is  dried  varies  considerably  from  year  to  year  according 
to  changes  in  the  market  for  fresh  and  canned  fruits.  From  30  to  40 
per  cent  of  the  peach  and  apricot  crops  are  dried  normally  and  of  pears 
usually  not  over  10  per  cent.  Over  90  per  cent  of  the  figs  and  raisin 
grapes  are  dried  and  the  quantity  of  prunes  not  dried  is  negligible. 


TABLE   1 

Tonnage  and  Value  of  Sun-Dried  Fruits  for  1923 


Dry  tons* 

Estimated  farm  value 

Per  pound 

Total 

Apricots 

30,000 

9,500 

26,000 

2,000 

131,000 

280,000 

20c 

7c 

10c 

10c 

7c 

4c 

$12,000,000 

Figs 

1,330,000 

Peaches 

5,200,000 

Pears 

400,000 

Prunes 

18,340,000 

Raisins 

22,400,000 

Total 

478,500 

$59,670,000 

Compiled  by  Dried  Fruit  Association  of  California. 


TABLE  2 
Acreages  of  Certain  Fruits  in 

L924* 

Bearing 

Non-bearing 

Total 

Apricots 

68,887 

23,982 

120,947 

45,407 

138,558 

297,164 

21,022 
24,269 
28,455 
24,593 
47,261 
60,291 

89,909 

Figs 

48,251 

Peaches 

149,402 

Pears 

71,000 

Prunes 

185,819 

Raisin  Grapes 

357,455 

1924. 


Compiled  by  E.  E.  Kaufman,  Calif.  Coop.  Crop  Reporting  Service.    Includes  acreages  planted  in 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING   FRUIT 


From  the  large-non-bearing  acreages  given  in  Table  2,  to  which 
should  be  added  extensive  plantings  made  in  1925,  it  is  evident 
that  the  production  of  dried  fruits  must  inevitably  increase.  If 
fresh  shipment  and  canning  do  not  keep  pace  with  the  increasing 
production,  it  may  become  necessary  to  dry  a  greater  proportion  of 
the  fruit  crop  than  formerly.  The  production  of  dried  fruits  is  also 
expanding  in  other  parts  of  the  world,  notably  Australia  and  South 
Africa.  At  present,  the  rate  of  financial  exchange  and  other  condi- 
tions resulting  from  the  world  war  seriously  restrict  exports  of  dried 
fruits  from  the  United  States  and  moreover  permit  the  importation  of 
certain  dried  fruits  from  the  Mediterranean  countries.  The  amount 
of  dried  fruit  exports  and  imports  in  1923  can  be  seen  from  Table  3. 

TABLE  3 

United  States  Imports  and  Exports  of  Sun-Dried  Fruits 
(Fiscal  Year  1922-23) 


Tons  imported 

Tons  exported 

Apricots 

0 

18,293 

0 

0 

6,168 

9,462 

5,597 

Figs 

0 

Peaches 

2,793 

Prunes ....                                  

39,615 

Raisins 

46,981 

Currants 

0 

Total 

33,923 

94,986 

From  U.  S.  D.  A.  Year  Book,  1923. 


PBINCJPAL  LOCALITIES  AND  VAEIETIES  FOE  SUN-DEYING 

With  the  exception  of  the  extreme  northern  part  of  the  state  and 
the  mountainous  districts  of  the  Coast  Range  and  the  Sierra  Nevada, 
fruits  are  grown  and  dried  in  almost  every  agricultural  region  of 
California.  Some  districts  have  been  found  to  be  particularly  suited 
to  the  growing  of  certain  kinds  of  fruit  and  have  consequently  taken 
the  lead  in  the  production  of  these  fruits.  Likewise  certain  varieties 
because  of  higher  quality  or  yield  have  been  most  extensively  planted 
and  dried  and  have,  therefore,  become  the  trade  standard.  The  follow- 
ing paragraphs  give  briefly  for  each  fruit  the  principal  counties  and 
varieties,  the  usual  drying  season,  and  the  average  drying  ratios  and 
yields. 


b  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Apricots. — The  counties  producing  dried  apricots  are,  in  order  of 
importance :  Santa  Clara,  Ventura,  Riverside,  Los  Angeles  and  San 
Benito.  The  Sacramento,  San  Joaquin  and  Pajaro  valleys  also  con- 
tribute large  quantities.  The  principal  varieties  dried  are,  in  order  of 
importance:  Royal,  Blenheim,  Tilton  and  Moorpark.  To  be  suitable 
for  drying,  an  apricot  should  be  of  fair  size  and  rich  flavor  and  have 
a  uniform  golden  color.  In  the  interior  valleys,  the  drying  season 
begins  between  June  15  and  July  1,  while  in  the  coast  counties  picking 
rarely  begins  until  July  1  to  5.  The  acre  yield  varies  from  3  to  9 
fresh  tons,  averaging  between  5  and  6.  The  drying  ratio  will  vary 
from  as  low  as  4 :1  for  very  large  ripe  fruit  to  as  high  as  7  :1  for  small 
early  maturing  fruit,  and  averages  about  5:1.  The  normal  yield  of 
dried  fruit  is  from  1  to  1%  tons  per  acre.  For  further  information  see 
Circular  238  of  this  station — "The  Apricot  in  California." 

Peaches. — Peach  drying  is  most  largely  practiced  in  the  Sacramento 
and  San  Joaquin  valleys.  Some  peaches  are  dried  in  southern  Cali- 
fornia but  few  along  the  coast  or  in  the  foothills.  The  leading  counties 
in  order  of  importance  are :  Fresno,  Tulare,  Placer,  San  Bernardino 
and  Solano.  Only  firm  yellow  freestone  varieties,  principally  the 
Muir,  Lovell  and  Elberta,  are  dried  commercially.  In  the  San  Joaquin 
Valley  peach  drying  begins  as  early  as  July  15  for  Muirs  and  con- 
tinues into  September  for  Lovells.  In  the  Sacramento  Valley  most  of 
the  peaches  are  dried  during  August.  The  acre  yield  may  vary  from  ' 
5  to  20  fresh  tons,  and  averages  not  over  10  tons.  The  drying  ratio  of 
Muir  and  Lovell  varies  from  4 :1  to  5  :1,  while  the  Elberta  will  shrink 
from  6  :1  to  7  :1.  A  general  average  drying  ratio  would  be  about  5 :1. 
The  average  yield  of  dried  peaches  is  about  1%  tons  per  acre. 

Pears. — Bartlett  pears,  the  only  variety  dried,  are  grown  princi- 
pally in  Sacramento,  Solano,  Los  Angeles,  Santa  Clara,  San  Luis 
Obispo,  Yuba  and  Lake  counties.  Except  in  Lake  County  only  pears 
unsuited  to  fresh  shipment  or  canning  are  usually  dried.  Ordinarily 
windfall  pears,  bruised  or  blemished  but  otherwise  sound  are  used 
for  drying,  but  in  Lake  County  a  large  proportion  of  the  whole  crop 
is  dried,  which  makes  this  county  the  leader  in  quality  as  well  as  in 
quantity  of  dried  pears.  In  the  Sacramento  Valley  and  foothills  dry- 
ing begins  about  July  15  and  extends  throughout  August,  while  in  the 
north  coast  counties  it  begins  during  the  latter  half  of  August  and 
extends  through  September.  Pears  yield  from  10  to  20  tons  per  acre 
but  because  of  the  fact  that  in  most  localities  only  a  varying  portion 
of  the  crop  is  dried  no  exact  figures  for  the  acre  yield  of  dried  fruit 
can  be  given.     The  drying  ratio  varies  from  as  low  as  4:1  in  Lake 


Bull.  388]  PRINCIPLES    OF   SUN-DRYING   FRUIT  7 

County  to  as  high  as  7  :1  in  the  Sacramento  Valley,  averaging  for  the 
state  about  5  :1. 

Primes. — The  greatest  prune  acreage  is  to  be  found  in  the  valleys 
near  the  coast,  such  as  those  of  Santa  Clara,  Sonoma,  Napa  and  San 
Benito  counties.  The  acreage  in  the  Sacramento  and  San  Joaquin 
valleys  is  rapidly  increasing — Tulare,  Solano  and  Butte  being  leading 
counties.  The  most  important  variety  is  the  French  prune.  Other 
important  varieties  are :  Imperial,  the  largest  variety  and  grown  prin- 
cipally in  the  northern  coast  counties;  Sugar,  not  so  high  in  quality 
as  the  French,  but  a  heavy  bearer  in  the  interior  valleys;  Robe  de 
Sargeant,  similar  to  the  French.  In  the  warmer  sections,  drying  begins 
during  the  latter  part  of  August  and  extends  through  September,  but 
where  the  prunes  are  late  in  maturing  drying  may  commence  in  Sep- 
tember and  extend  well  into  October.  A  prune  orchard  will  produce 
from  3  to  10  tons  of  fresh  prunes  per  acre.  In  the  coast  counties  the 
drying  ratio  ranges  from  2  :1  to  2%  :1  and  in  the  interior  valleys  and 
southern  California  from  2%  :1  to  3  :1,  the  state  average  being  nearly 
2a/2  :1-  The  average  acre  yield  of  dry  prunes  is  two  tons.  For  further 
information  see  Bulletin  328  of  this  station,  "Prune  Growing  in 
California. ' ' 

Figs. — Most  of  the  dried  figs  are  produced  in  the  San  Joaquin 
Valley,  the  leading  counties  being  Fresno,  Tulare,  Merced,  Stanislaus 
and  Madera.  Some  figs  are  dried  in  the  Sacramento  Valley,  especially 
Mission  figs  in  Yolo  County.  The  most  important  variety  is  the  white 
Adriatic,  which  is  used  exclusively  for  drying.  The  next  in  import- 
ance is  the  Calimyrna,  which  is  being  extensively  shipped  and  canned 
as  well  as  dried.  The  third  variety  is  the  Black  Mission,  the  first  crop 
of  which  is  shipped  fresh  and  the  second  crop  dried.  The  Kadota  is 
used  primarily  for  preserving,  but  if  caprified  produces  a  fair  dried 
product.  Figs,  especially  those  which  produce  two  crops,  ripen  over 
a  long  season.  The  figs  drop  to  the  ground  when  high  in  sugar  and 
already  partially  dried  and  the  harvesting  season  extends  from  late 
July  to  the  beginning  of  cold  wet  weather  in  October  or  even  November. 
Calimyrna  orchards  produce  from  1  to  2  tons  and  Adriatic  and  Mission 
varieties  2  to  4  tons  of  dried  figs  per  acre,  the  average  for  the  Cali- 
myrna being  1.2  and  for  the  other  varieties  2.5  tons  per  acre.  The 
drying  ratio  of  figs  as  normally  harvested  for  drying  is  lower  than 
that  of  any  other  fruit,  rarely  exceeding  1%  :1.  However,  figs  picked 
for  fresh  shipment  or  canning  would  have  a  drying  ratio  of  about  3  :1. 

Raisins. — Over  half  the  grapes  grown  in  California  are  of  raisin 
varieties,  95  per  cent  being  produced  in  the   San  Joaquin  Valley. 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Fresno  County,  which  produces  half  the  world's  supply  of  raisins, 
omitting  currants,  is  first,  followed  by  Tulare,  Kings,  Madera  and 
Merced  counties.  Sutter,  Yolo  and  Yuba  counties  produce  notable 
quantities  of  seedless  raisins  and  small  quantities  are  produced  in 
southern  California.  The  varieties  used  for  raisins  are,  in  order  of 
importance:  Sultanina  (Thompson  Seedless),  Muscat,  and  Sultana. 
Wine  and  table  varieties  are  dried  to  some  extent,  but  are  generally 
referred  to  as  dried  grapes  rather  than  as  raisins.  The  raisin  season 
extends  throughout  September  and  October,  according  to  the  time  of 
maturity  for  a  particular  variety  or  district.  Good  vineyards  yield 
from  5  to  15  tons  of  grapes  per  acre.  The  drying  ratio  is  regulated 
by  the  sugar  content  and  may  vary  from  3:1  to  4:1,  averaging  3%  :1. 
The  average  yield  of  raisins  is  from  %  to  1%  tons  per  acre,  although 
many  vineyards  produce  as  high  as  2%  to  3  tons. 

PKINCIPLES  OF  SUN-DKYING  FEUIT 

The  methods  and  equipment  used  in  sun-drying  fruit  are  still  very 
much  the  same  as  those  adopted  in  the  beginning  of  the  industry.  Very 
little  scientific  study  has  been  given  the  principles  and  practices  and 
little  exact  information  has  been  published.  The  demand  for  such 
information  is  growing  greater  and  more  insistent.  Many  persons 
without  previous  experience  are  engaging  in  the  growing  and  drying 
of  fruits  and  even  experienced  growers  are  realizing  more  than 
formerly  that  a  thorough  understanding  of  the  principles  of  drying 
coupled  with  knowledge  of  the  most  successful  methods  and  equip- 
ment are  essential  to  the  economical  production  of  dried  fruits  of 
quality. 

If  the  production  of  dried  fruits  in  California  is  to  be  profitably 
maintained  in  spite  of  constantly  increasing  production,  both  domestic 
and  foreign,  it  is  imperative  that  the  quality  of  our  products  be  of 
the  highest.  The  individual  grower  is  the  most  important  link  in  the 
chain  which  produces  and  markets  dried  fruits  and  unless  he  gives  the 
same  care  to  the  production  of  his  dried  fruit  as  to  the  food  on  his 
own  table,  he  will  not  obtain  the  sale  value  his  product  should  have. 
The  principles  and  practices  are  simple  and  readily  grasped  but  must 
be  understood  and  followed  in  order  to  get  the  best  results. 

Legend  for  color  plate: 

Fig.  1. — Types  of  sun  dried  fruits  (actual  size  of  grades) 

1.  Muir  Peach  (Extra  Fancy)  4.  Bartlett  Pear  (Choice) 

2.  French  Prune  (50/60)  5.  Adriatic  Fig  (Extra  Fancy) 

3.  Eoyal  Apricot  (Choice)  6.  Calimyrna  Fig  (Extra  Fancy) 


BULL.  388]  PRINCIPLES    OF   SUN-DRYING   FRUIT  9 

The  writers  have  supplemented  several  years  of  experience  in  fruit 
drying  by  an  extensive  survey  of  dry -yards  in  all  sections  of  the  state. 
Many  differences  in  methods  and  equipment  were  noted,  some  caused 
by  well  defined  climatic  or  other  conditions  while  the  reasons  for  other 
differences  were  uncertain.  The  following  pages  present  what  may 
be  termed  ' '  Standard  Methods  of  Sun-drying  Fruits. ' '  It  is  not  to  be 
expected  that  these  directions  will  fit  exactly  each  individual  case  but 
it  is  hoped  that  they  will  serve  as  a  general  guide  for  all  growers  who 
desire  to  dry  their  fruits  in  the  most  efficient  manner. 

EELATION  OF  CULTUEAL  PRACTICES  TO  QUALITY  OF  DEIED  FEUITS 

The  quality  of  dried  fruits  does  not  depend  alone  on  the  treatment 
after  picking  but  reflects  the  management  of  the  orchard  or  vineyard 
throughout  the  year.  Conscientious  application  of  the  best  cultural 
practices  of  cultivation,  irrigation,  fertilization,  pruning,  etc.,  is  essen- 
tial to  the  production  of  clean  fruit  of  large  size  and  good  quality. 
Proper  spraying  is  often  necessary  to  obtain  fruit  free  from  defects 
due  to  disease  or  insect  attack.  Dried  fruit  of  the  larger  sizes  and 
fine  quality  is  always  in  demand  at  good  prices  while  dried  fruit  of 
poor  quality  and  small  size  is  generally  difficult  to  dispose  of  even  at 
much  lower  prices.  It  is  important,  therefore,  that  each  and  every 
grower  exert  all  reasonable  effort  toward  the  production  of  the  best 
quality,  not  only  for  his  personal  profit,  but  in  order  that  the  markets 
for  California  dried  fruits  may  be  strengthened  and  maintained. 

Thinning  to  increase  size  is  a  very  important  operation  with 
apricots  and  peaches.  Small  fruit  is  more  expensive  to  handle,  shrinks 
more  in  drying  and  brings  a  lower  price.  The  following  figures 
furnished  by  the  California  Peach  and  Fig  Growers'  Association,  indi- 
cate the  financial  advantages  of  thinning.  Thirteen  peaches  (twenty- 
six  halves)  make  one  pound  of  extra  fancy  dried  peaches  bringing  17 
cents  per  pound  while  fifty-four  peaches  (one  hundred  and  eight 
halves)  are  required  to  make  one  pound  of  standard  dried  peaches 
bringing  only  10  cents  per  pound.  The  small  peaches  contain  7  to  9 
per  cent  of  pits  while  the  large  peaches  lose  only  5  per  cent  in 
pitting.  To  produce  one  pound  of  dried  peaches  of  standard  grade 
necessitates  the  picking,  cutting  and  drying  of  four  times  as  many 
peaches  as  are  required  to  produce  one  pound  of  extra  fancy  dried 
peaches.  The  cost  of  cutting  "Standards"  is  about  94  c  per  dry  pound 
as  compared  to  %c  per  dry  pound  of  ' '  Extra  Fancy, ' '  and  the  picking 
cost  for  small  peaches  is  half  again  as  great  as  for  large.  The  smaller 
sizes,  are  therefore,  more  expensive  to  produce  and  the  price  obtained 
is  much  lower. 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Comparative  observation  on  the  effects  of  thinning  apricots,  by 
Farm  Advisor  C.  C.  Staunton  of  Ventura  County  in  1923,  showed  a 
value  for  the  dried  apricots  resulting  from  each  box  of  fresh  fruit 
from  the  thinned  plots  of  $1.22  as  compared  with  79  cents  for  the 
dried  fruit  from  adjacent  unthinned  plots.  This  gain  of  over  50  per 
cent  in  value  was  principally  due  to  the  higher  prices  received  for 
the  larger  sizes.  The  unthinned  fruit  consisted  entirely  of  Standards 
(the  smallest  size-grade).  The  methods  of  thinning  deciduous  fruits 
are  described  in  Circular  258  of  this  station. 

EIPENESS  OF  FKUIT  AND  METHODS  OF  PICKING 

Fruit  intended  for  drying  should  be  thoroughly  matured.  With 
the  exception  of  pears,  no  fruit  should  be  picked  for  drying  until  it 
has  developed  its  full  ripe  color  and  flavor  and  has  reached  its  maxi- 
mum sugar  content.  When  in  prime  condition  for  eating,  fruit  is  also 
in  prime  condition  for  drying  but  not  before. 

The  hard  partially  green  fruit  required  for  commercial  canning 
or  fresh  shipment  is  entirely  unsuitable  for  drying.  Such  fruit,  when 
dried,  yields  a  product  of  low  grade,  lacking  in  color  and  flavor, 
excessively  shrivelled  and  curled  up  and,  because  of  its  deficiency  in 
sugar,  always  gives  a  lower  yield  of  dried  product.  The  effect  of 
maturity  on  the  drying  ratio  of  peaches  and  apricots  is  illustrated  in 
Table  4.  In  each  case  the  fruit  was  picked  at  one  time  from  a  small 
group  of  trees  at  the  University  Farm,  graded  for  maturity  and  all 
lots  reduced  to  the  same  degree  of  dryness. 

TABLE  4 

Effect  of  Maturity  on  the  Drying  Eatio  of  Peaches  and  Apricots 


Condition 


Blenheim 

apricots. 

Drying  ratio 


Muir  peaches 


Drying  ratio 


Per  cent  of  sugar 


Soft  ripe 

Firm  ripe 

Hard  ripe  to  green 


4.16:1 
4.50:1 
6.40:1 


4.86:1 
4.64:1 
5.11:1 


48.5 
48.5 
45.0 


Over-ripeness  in  fruits  that  require  cutting  is  also  to  be  avoided 
because  very  soft  fruit  is  difficult  to  cut  and  dry  without  losing  its 
shape  and  forms  dark  colored  "slabs"  which  stick  tight  to  the  trays 
and  bring  a  low  price. 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


11 


Pears  do  not  ripen  satisfactorily  on  the  tree  and  they  are,  there- 
fore, always  picked  green  and  allowed  to  ripen  in  boxes  or  bins  in  the 
shade.  This  method  results  in  a  firm  ripe  pear  and  the  best  dried 
product. 

Prunes  normally  drop  to  the  ground  when  mature  but  in  some 
sections  they  may  remain  on  the  tree  after  reaching  maturity.  In 
such  cases  it  becomes  necessary  to  knock  the  fruit  to  the  ground  for 
gathering.  Since  prunes  continue  to  increase  considerably  in  sugar 
content  until  maturity  and  normal  dropping  it  is  advisable  to  delay 
knocking  as  long  as  possible  in  order  to  secure  the  maximum  yield  of 
dark  skinned,  fine  flavored  fruit. 

The  yield  and  quality  of  raisins  bear  a  direct  relation  to  the  Balling 
degree  (sugar  content)  of  the  grape  juice.  To  obtain  raisins  of  first 
quality,  Muscat  grapes  should  not  be  picked  below  25°  Balling,  or 
Sultanina  grapes  below  23°  Balling.  The  higher  the  Balling  degree 
of  the  grapes  at  picking,  the  less  will  be  the  shrinkage  during  drying, 
the  greater  will  be  the  acre  yield  of  raisins  and  the  higher  will  be  the 
percentage  of  the  larger  sizes,  as  illustrated  by  observations  on  Muscat 
raisins  at  the  Kearney  Vineyard,  given  in  Table  5. 

In  any  case  raisin  grapes  should  not  be  picked  for  drying  until 
such  time  as  they  have  attained  the  highest  possible  sugar  content 
consistent  with  safety  in  completing  drying  in  favorable  weather. 
While  the  flavor  and  color  of  grapes  indicate  their  condition  fairly 
well,  the  most  reliable  index  of  maturity  is  the  sugar  percentage  of 
the  juice.  This  is  easily  and  quickly  measured  by  the  use  of  a  Balling 
hydrometer  which  floats  in  a  sample  of  the  grape  juice  at  a  level 
indicating  the  percentage  of  sugar.  While  a  Balling  degree  of  25° 
is  most  desirable,  it  is  often  necessary  in  certain  sections  or  in  certain 
years  to  pick  the  grapes  at  22°  to  24°  Balling. 


TABLE  5 

Eelation  of  Sugar  Content  of  Grapes  to  the  Drying  Ratio,  Yield  and 

Grades  of  Muscat  Eaisins* 


Balling 

Drying 
ratio 

Pounds 
per  acre 

Percentage  of  grades 

degree  of 
juice 

4  Crown 

3  Crown 

2  Crown 

Seedless 

Waste 

18.6 

4.6 

2950 

7.5 

66.0 

23.3 

1.6 

2.1 

20.2 

4.3 

3050 

7.5 

.68.8 

21.5 

1.1 

1.0 

21.8 

3.9 

3032 

8.3 

70.2 

19.0 

1.5 

1.0 

23.6 

3.6 

3191 

12.8 

68.7 

15.4 

2.4 

0.8 

24.0 

3.5 

3414 

20.3 

64.8 

13.0 

1.4 

0.6 

26.5 

3.3 

4363 

30.4 

56.6 

12.3 

0.7 

0.2 

Reported  by  Professor  F.  T.  Bioletti. 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

With  the  exception  of  prunes  and  figs,  which  generally  fall 
naturally  to  the  ground  when  mature,  fruits  should  be  picked  from 
the  tree  and  not  knocked  to  the  ground  for  gathering.  When  fruit  is 
knocked  or  shaken  from  the  tree  a  certain  amount  of  green  fruit  is 
inevitably  brought  down  with  the  ripe  and  the  fruit  becomes  more  or 
less  bruised  and  dirty  in  striking  the  branches  or  ground  in  its  fall. 
When  a  few  very  hot  days  cause  the  rapid  ripening  of  an  entire 
orchard  of  apricots,  or  peaches,  hand  picking  may  become  too  slow, 
especially  if  labor  is  inadequate.  Under  such  conditions  it  becomes 
necessary  to  gather  the  fruit  more  rapidly  by  first  knocking  it  to  the 
ground.  Striking  the  branches  with  poles  may  injure  the  fruit  spurs. 
It  is  safer  to  shake  each  branch  by  the  use  of  a  long  pole  provided  with 
an  iron  hook.  Small  trees  can  often  be  sufficiently  shaken  directly  by 
hand.  Experienced  pickers  can  obtain  all  the  ripe  fruit  by  this  method 
without  bringing  down  much  green  fruit.  Where  the  soil  is  soft 
and  loose  in  texture  and  has  been  well  smoothed  before  picking,  injury 
to  the  fruit  is  minimized.  In  some  sections  a  large  canvas  is  spread 
under  the  tree  which  not  only  prevents  the  fruit  from  coming  into 
contact  with  the  soil  but  greatly  facilitates  transferring  the  fruit  to 
lug  boxes.  In  general,  however,  the  most  successful  growers  have 
found  that  the  slightly  greater  cost  of  hand  picking  which  makes  it 
possible  to  exclude  immature  fruit  is  overbalanced  by  the  better  quality 
and  greater  yield  of  the  dried  product. 

Wind-falls  should  be  picked  up  frequently,  preferably  every  morn- 
ing, as  the  bruised  fruit  deteriorates  very  rapidly  when  lying  on  the 
ground  in  the  sun. 

PREPARATIONS  FOR  DRYING 

Cutting. — Pears,  apricots  and  peaches  are  cut  in  half  and  the  last 
two  pitted.  Halved  fruits  have  become  the  trade  standard  because  of 
their  superior  appearance  and  the  greater  readiness  with  which  they 
may  be  prepared  for  the  table.  Furthermore,  halved  fruits  absorb 
sulfur  fumes  and  dry  much  more  rapidly  than  whole  fruits.  Internal 
defects  caused  by  split  pits,  worms,  etc.,  are  revealed  and  such  fruits 
trimmed  or  discarded. 

Cutting  is  invariably  done  by  hand  and  should  result  in  two  equal 
halves  with  cleanly  cut,  smooth  edges.  Various  types  of  special  cutting 
and  pitting  knives  have  been  introduced  but  possess  no  advantages 
over  an  ordinary  sharp  knife  in  the  hands  of  experienced  cutters. 
Cutting  machines  have  been  introduced  but  have  not  so  far  been 
adopted  in  dry  yards.  For  satisfactory  results  the  fruit  must  be  fed 
into  the  machines  by  hand,  after  which  as  in  hand  cutting  the  halved 
fruit  must  be  spread  on  trays,  cut  surface  up. 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


13 


FRUIT  DRYING 
ORDER  OF  OPERATIONS 


TEARS 


PRUNES 


PEACHES                             , 

CRAPES 

HHniuiuti)         OH 

<JR           

APRICOTS 

FIGS 

STORING 


Fig.  2. — Fruit  drying,  order  of  operations. 


14  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

Apricots  can  be  dried  whole  after  lye  dipping  and  sulfuring  but 
despite  their  excellent  flavor  and  lower  cost  of  preparation  are  so  far 
in  little  demand  and  bring  a  comparatively  low  price.  The  pits  of 
apricots  may  be  forced  out  by  pressure  between  the  thumb  and  fore- 
finger after  the  fruit  has  been  softened  by  thorough  sulfuring  but  the 
product  is  unattractive  and  of  little  commercial  importance. 

Most  fruits  are  not  peeled  before  drying.  The  fuzzy  skin  of  peaches 
is  preferably  removed  after  drying  by  a  patented  process.  Peaches 
may  be  lye-peeled  as  for  canning  or  the  skins  may  be  slipped  off  after 
sulfuring  but  such  peeling  reduces  the  yield  and  increases  the  cost  of 
the  product. 

The  pits  should  be  collected  and  sun-dried.  Apricot  pits  are  a 
valuable  source  of  by-products.  An  edible  fixed  oil,  the  volatile  oil  of 
bitter  almonds  and  macaroon  paste  are  being  manufactured  from  the 
kernels.  For  this  purpose  the  dry  pits  have  been  bringing  about  $40 
a  ton.  Peach  pits  contain  a  much  smaller  percentage  of  kernels  and 
are  not  now  in  demand  for  by-products  but  make  an  excellent  fuel 
which  may  bring  as  high  as  five  to  ten  dollars  a  ton. 

Dipping. — Prunes  and  some  grapes  are  immersed  in  a  hot  dilute 
alkaline  solution  for  a  few  seconds  before  drying.  Dipping  cleanses 
the  fruit  and  removes  the  waxy  bloom.  This  results  in  a  clean,  glossy 
product.  The  hot  alkaline  solution  produces  minute  cracks  or  checks 
in  the  skin  which  greatly  facilitate  the  evaporation  of  moisture  during 
drying.  Ordinarily,  grape  dipping  is  largely  confined  to  the  Sultana 
and  Sultanina  (Thompson  Seedless)  varieties  grown  in  the  Sacra- 
mento Valley  where  it  aids  in  securing  rapid  and  complete  drying. 
If  dipping  is  followed  by  sulfuring,  the  sulfur  fumes  penetrate  the 
fruit  more  rapidly  and  completely.  Dipping  should  be  followed  by 
rinsing  in  fresh  water  to  free  the  fruit  from  adhering  lye  solution 
which  is  invariably  more  or  less  dirty. 

White  figs  are  frequently  dipped  in  a  cold  solution  containing  salt 
and  sometimes  lime.  The  function  of  this  process  is  to  cleanse  the 
figs  and  make  them  moist  for  more  efficient  sulfuring. 

Sulfuring. — Apricots,  peaches,  pears,  Silver  prunes  and  some 
grapes  are  exposed  to  the  fumes  of  burning  sulfur  after  cutting  or 
dipping  and  before  drying.  When  sulfur  burns  it  combines  with  the 
oxygen  of  the  air  to  form  a  gas,  sulfur  dioxide.  This  gas  has  the 
property  of  dissolving  in  water  to  form  a  mild  acid  known  as  sulfurous 
acid.    This  action  may  be  represented  graphically  as  follows. 

S  +  02  =  S02  +  H20  ~  H2S03 
Sulfur  +  Oxygen  =  Sulfur  Dioxide  +  Water  =  Sulfurous  Acid. 


Bull.  388]  PRINCIPLES    OF   SUN-DRYING   FRUIT  15 

Without  the  presence  of  adequate  moisture,  sulfurous  acid  cannot  be 
formed  in  sufficient  amounts  to  secure  the  desired  preserving  action 
on  the  fruit.  For  this  reason  it  is  highly  desirable  to  wash  or  sprinkle 
the  fruit  with  water  before  sulf uring  in  order  that  the  surface  may  be 
in  a  moist  condition  to  readily  absorb  the  sulfur  dioxide  gas.  It  has 
also  been  observed  that  the  higher  the  temperature  naturally  obtained 
in  a  sulfur  house,  the  more  rapid  and  thorough  will  be  the  action  of 
the  sulfur  dioxide  on  the  fruit. 

Sulfurous  acid  in  small  amounts  is  a  harmless  preservative  and 
without  its  use  the  high  commercial  quality  of  California  dried  fruits 
could  not  have  been  developed.  Numerous  substitutes  for  sulfur  have 
been  tried  but  none  have  been  successful.  Sulfur  is  the  standard  and 
practically  the  only  preservative  for  dried  fruits.  Although  con- 
siderable amounts  of  sulfurous  acid  are  formed  in  the  fruit  during 
sulfuring  the  greater  part  of  this  is  evaporated  during  drying,  and 
there  is  a  further  small  but  steady  loss  during  storage  after  drying. 

Part  of  the  sulfur  dioxide  absorbed  by  the  fruit  combines  with  the 
sugar  and  other  compounds  of  the  fruit  in  such  a  way  that  it  cannot 
be  separated  from  the  fruit  without  destroying  the  merchantability  of 
the  product. 

However,  if  the  amount  of  sulfur  burned  much  exceeds  that 
required  to  preserve  a  natural  color,  an  excessive  absorption  and  reten- 
tion of  sulfur  dioxide  gives  the  dried  product  a  sulfurous  taste  which 
is  objectionable  to  most  consumers.  Therefore,  it  behooves  every 
grower  to  restrict  his  use  of  sulfur  to  the  minimum  amount  found 
necessary  to  properly  preserve  the  color  of  the  fruit  in  order  to 
maintain  the  good  reputation  of  California  dried  fruits. 

The  principal  effects  of  sulfuring  are  briefly  described  as  follows : 
It  ' '  fixes  "  or  "  sets ' '  the  natural  colors  of  fruits  and  prevents  darken- 
ing by  oxidation  during  drying  (see  fig.  1).  This  action  is  sometimes 
termed  bleaching.  This  is  incorrect,  although  dark  spots  on  light 
colored  fruits  are  sometimes  temporarily  bleached.  Sulfuring  kills 
insects  and  the  sulfurous  acid  prevents  fermentation  and  molding  dur- 
ing drying  and  storage.  The  absorption  of  sulfurous  acid  ruptures  the 
cells  of  the  fruit  more  or  less  and  draws  moisture  into  the  pit  cavity. 
This  results  in  a  more  rapid  evaporation  of  moisture  during  drying. 

PRESERVATION  BY  DRYING 

Sun-drying,  or  the  evaporation  of  moisture  by  the  action  of  solar 
heat  and  natural  air  currents,  is  the  oldest  form  of  food  preservation. 
Since  the  beginning  of  history,  fruits,  vegetables,  cereals,  meats  and 
fish  have  been  preserved  in  the  dried  form.     If  properly  understood, 


16  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

sun-drying  is  at  once  the  simplest  and  most  economical  method  of  food 
preservation.  By  this  means  vast  quantities  of  fresh  fruits  ripening 
during  a  period  of  a  few  weeks  are  rapidly  reduced  to  a  durable  con- 
centrated form  for  subsequent  transportation  throughout  the  year  to 
all  markets  of  the  world. 

A  certain  amount  of  moisture  is  essential  to  the  development  of  the 
microorganisms  such  as  yeasts,  molds  and  bacteria  which  are  the  cause 
of  spoiling  and  decay.  Fresh  fruits  contain  from  60  to  95  per  cent  of 
water  and  spoil  rapidly,  but  if  their  moisture  content  be  reduced  by 
evaporation  to  between  20  and  25  per  cent,  such  spoiling  can  not  occur. 
In  practice,  however,  growers  must  dry  fruits  to  a  moisture  content 
of  16  to  20  per  cent  in  order  that  the  fruit  will  be  sufficiently  dry  to 
permit  of  the  absorption  of  5  to  10  per  cent  moisture- during  the  neces- 
sary processing  in  the  packing  house,  without  increasing  the  moisture 
content  to  an  amount  which  permits  spoiling.  It  is  not  necessary  to 
evaporate  all  the  water  in  the  fruit,  because  when  sufficient  water 
has  evaporated  that  which  remains  forms  with  the  sugar  in  the  fruit, 
what  may  be  considered  a  concentrated  syrup.  The'  concentration  of 
sugar  becomes  so  high  that  it  acts  as  a  natural  preservative  in  which 
microorganisms  are  unable  to  develop.  If  the  fruit  has  been  sulfured 
it  may  be  packed  at  a  higher  moisture  content  because  of  the  added 
preservative  action  of  the  sulfurous  acid. 

As  a  result  of  sun-drying,  fruits  undergo  material  changes  in  color, 
flavor  and  texture  to  which  the  consumer  has  become  accustomed  and 
which  have  therefore  become  the  trade  standards.  No  loss  of  food 
value  results  from  proper  drying. 

Evaporation  means  the  change  of  water  from  the  liquid  to  the 
vapor  form.  The  heat  required  for  this  change  may  be  obtained  by 
direct  radiation  from  the  sun  or  indirectly  from  air  currents  heated 
by  the  sun's  rays.  Without  the  absorption  of  a  certain  definite  amount 
of  heat  for  each  pound  of  water  evaporated,  drying  can  not  take  place. 
The  water  vapor  driven  off  by  this  heat  is  absorbed  by  the  surrounding 
air  but  a  given  volume  of  air  at  a  given  temperature  can  only  absorb 
a  certain  amount  of  water  vapor.  This  emphasizes  the  importance  of 
air  circulation  in  removing  the  partially  moisture  laden  air  from 
immediate  contact  with  the  product  being  dried  and  in  replacing  it 
with  drier  air  so  that  the  air  may  not  become  saturated  and  prevent 
further  evaporation.  Summarizing  the  factors  governing  sun-drying, 
it  may  be  said  that  the  rate  of  drying  will  be  the  greater : 

1.  The  higher  the  temperature  of  the  air, 

2.  The  lower  the  relative  humidity  of  the  air, 

3.  The  more  rapid  the  circulation  of  the  air. 


Bull.  388]  PRINCIPLES  of  sun-drying  fruit  17 

While  in  artificial  drying  these  factors  can  be  satisfactorily  controlled, 
little  control  in  sun-drying  is  possible  except  that  in  very  hot  weather 
the  product  may  be  dried  by  air  currents  in  the  shade,  thereby  avoid- 
ing the  more  intense  heat  of  the  direct  sunshine.  In  sun-drying  most 
of  the  evaporation  takes  place  during  the  day  since  at  night  the  tem- 
perature of  the  air  is  lower,  the  relative  humidity  higher  and  the 
amount  of  air  movement  generally  less. 

After  preparation,  the  trays  of  fruit  are  nearly  always  spread  on 
the  ground  in  the  direct  sunshine  for  one  or  more  days  according  to 
the  temperature  and  the  particular  practice  followed.  The  first 
direct  exposure  warms  up  the  fruit  and  quickly  dries  the  surface.  In 
addition,  the  sunlight  causes  what  has  been  termed  an  "after- 
ripening"  of  the  color  of  fruits.  This  means  that  a  uniform  deep 
rich  color  is  acquired  by  all  the  pieces  of  fruit.  Fruit  dried  exclusively 
in  the  shade  retains  more  nearly  the  original  uneven  colors  of  the 
fruit.  Immediately  after  this  first  part  of  the  drying,  which  results 
in  the  evaporation  of  from  one  to  three-fourths  of  the  moisture,  the 
trays  are  stacked  so  that  the  remainder  of  the  drying  may  proceed 
more  slowly  in  the  shade.  This  method,  known  as  stack  drying,  has 
several  advantages.  The  fruit  will  often  be  freer  from  wind  blown 
dust.  Protection  from  the  direct  sunshine  results  in  a  softer  skin 
and  prevents  excessive  darkening  and  loss  of  flavor.  Since  the  final 
evaporation  proceeds  more  slowly,  the  dryness  of  the  pieces  of  various 
sizes  more  nearly  approaches  equality  and  over-drying,  with  conse- 
quent loss  in  weight,  is  avoided. 

Drying  Ratio. — The  term  drying  ratio  is  commonly  used  to  desig- 
nate the  relation  between  the  weight  of  the  fresh  fruit  and  the  weight 
of  the  dried  fruit  obtained  from  it.  It  is  expressed  as  a  ratio  of  the 
number  of  pounds  of  fresh  fruit  required  to  produce  one  pound  of 
dried  fruit,  as  for  example,  a  5 :1  drying  ratio  for  apricots.  This 
ratio  includes  all  losses  in  weight,  chief  among  which  are  evaporation 
of  water  during  drying  and  losses  in  preparation  such  as  pitting,  trim- 
ming, coring,  etc.  It  also  includes  incidental  losses  which  can  be 
largely  eliminated  by  careful  practice.  Among  these  should  be  men- 
tioned loss  of  material  during  preparation ;  spilling  of  juice  from  the 
cups  of  sulfured  fruits ;  loss  in  weight  by  evaporation  of  carbon  dioxide 
and  alcohol  formed  by  the  partial  fermentation  of  sugar  during  drying 
of  unsulfured  fruits.  This  loss  in  weight  because  of  fermentation  has 
been  found  to  be  considerable  in  prune  drying  and  is  greatly  increased 
by  unfavorable  drying  weather. 


18  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

STORAGE  AFTER  DRYING 
Determining  Proper  Degree  of  Dryness. 

The  characteristics  of  fruit  when  properly  dried  cannot  be 
explained  adequately  here  and  are  to  be  learned  by  experience  rather 
than  from  printed  directions.  In  general,  however,  it  may  be  said 
that  fruit  is  sufficiently  dry  when  it  is  no  longer  soft,  puffy  or  juicy  in 
the  center  and  yet  is  not  so  dry  and  hard  as  to  rattle  when  the  tray 
is  shaken.  It  should  not  be  possible  to  separate  the  skin  by  hand 
rubbing.  It  must  be  firm  and  yet  uniformly  soft  and  pliable  like 
chamois  skin.  When  a  handful  of  the  fruit  is  squeezed  together 
tightly  and  then  released  the  individual  pieces  should  drop  apart 
readily.  Although  it  is  a  fundamental  fact  that  the  lower  the  moisture 
content  the  better  will  be  the  keeping  quality  of  the  dried  fruit, 
excessive  drying  merely  results  in  a  loss  of  weight  and  therefore  of 
profit.  Since  most  processing  methods  necessarily  add  a  little  water 
to  the  fruit  before  packing  it  is  obvious  that  the  fruit  must  be  suffi- 
ciently dry  to  absorb  this  added  moisture  without  exceeding  the  limits 
for  spoilage. 

Equalization  of  Moisture  During  Storage. 

It  is  impossible  to  have  all  the  pieces  of  fruit  on  a  tray  dried  to  the 
same  degree  at  the  same  time  because  of  the  lack  of  uniformity  in  the 
size,  composition  and  preparation  of  individual  fruits.  Therefore, 
when  most  of  the  fruit  is  considered  sufficiently  dry  for  storage  it  is 
emptied  into  large  boxes  or  bins  to  undergo  an  equalization  of  moisture, 
commonly  referred  to  as  ' '  sweating. ' '  During  this  process  the  moisture 
contents  of  over-dried  and  under-dried  pieces  of  fruit  are  equalized 
either  by  direct  absorption  through  contact  or  by  translocation  of  the 
moisture  by  evaporation  and  absorption.  This  equalization,  which 
also  blends  and  standardizes  the  quality  of  the  product,  must  precede 
the  final  processing  and  packing. 

The  storage  place  should  be  clean,  dry,  dark,  well  ventilated  and 
protected  from  rodents  and  insects  so  that  the  fruit  will  suffer  little 
or  no  deterioration  during  storage.  As  soon  as  the  necessary  equaliza- 
tion has  been  accomplished,  which  will  usually  be  within  two  or 
three  weeks,  it  is  generally  advisable  to  deliver  the  product  at  the  first 
opportunity  to  the  packing  house  for  grading  and  storage. 

The  processing  and  packing  of  dried  fruits  is  ordinarily  not  con- 
ducted by  the  grower,  but  is  a  distinct  and  separate  operation  con- 
ducted in  large  centrally  located  packing  houses  by  persons  experienced 
in  the  methods.  This  phase  of  the  industry  is  not  described  in  this 
publication. 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


19 


Fig.  3. — Typical  dry  yard  scenes. 


20  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


EQUIPMENT  FOR  SUN-DRYING  FRUITS 
DEY  YAEDS 

With  the  exception  of  undipped  grapes  which  are  dried  between 
the  rows  in  the  vineyard  and  some  figs  which  are  cured  in  the  orchard, 
all  fruits  are  brought  to  an  open  dry -yard  for  preparation  and  drying. 
The  concentration  of  all  operations  at  one  place  set  aside  for  the 
purpose  is  economical  of  time  and  labor. 

The  dry-yard  should  be  conveniently  located  with  respect  to  the 
orchard  or  vineyard  and  away  from  all  dusty  roads  and  barn  yards. 
Roads  required  for  hauling  fruit  to  and  from  the  dry-yard  should  be 
so  located  that  the  prevailing  winds  will  blow  the  dust  away  from  and 
not  over  the  drying  fruit.  The  dry -yard  should  have  a  sunny  exposure 
free  from  shading  trees,  and  preferably  a  slight  slope  toward  the 
south.  Larger  yards  where  cars  and  tracks  are  needed  should  be 
sufficiently  level  to  permit  their  use.  The  area  of  dry-yard  required 
will  vary  from  one-third  to  one  acre  for  each  ten  acres  of  orchard  or 
vineyard ;  according  to  the  orchard  yield  and  the  speed  of  drying.  In 
general,  1  to  20  is  a  safe  average  ratio. 

The  surface  of  the  ground  should  be  handled  in  such  a  way  as  to 
prevent  dust  blowing  on  the  fruit  during  drying.  Some  excellent  dry- 
yards,  as  illustrated  in  fig.  3,  are  never  cultivated  but  the  ground  is 
allowed  to  become  solidly  packed  and  free  from  loose  dust  or  vegeta- 
tion. A  more  common  practice  is  to  grow  grain  or  hay  and  spread 
the  trays  on  the  closely  cut,  well  raked  stubble  after  harvesting.  This 
usually  necessitates  the  relaying  of  portable  tracks  each  year,  but 
realizes  a  return  from  the  crop  harvested.  The  stubble  should  never 
be  burned  before  the  drying  season  as  this  causes  the  fruit  to  become 
unsightly  because  of  wind  blown  bits  of  charred  straw.  A  closely  cut 
and  not  recently  irrigated  alfalfa  field  is  very  satisfactory  for  peaches 
and  apricots  but  for  the  slower  drying  prunes  or  grapes  in  cooler 
sections  may  unduly  increase  the  drying  time.  The  contamination  of 
dry -yards  and  drying  fruit  by  animals  or  poultry  must  be  carefully 
guarded  against  by  adequate  fencing. 

Foreign  matter  which  lodges  on  the  surface  of  cut  fruits  during 
drying  can  not  be  satisfactorily  removed  in  the  packing  house  and, 
therefore,  seriously  lowers  the  quality  of  the  product.  Consequently 
the  dry-yard  should  be  so  prepared  and  managed  as  to  minimize 
contamination  of  the  fruit  during  drying. 


Bull.  3S8] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


21 


'I 

H 

£      Hs 


3  fi 


O-    o 


o     CD 
o    " 


22  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

All  but  the  smallest  yards  should  be  provided  with  a  system  of 
tracks  and  cars  for  moving  the  trays  of  fruit  between  the  various  steps 
in  preparation  as  well  as  to  and  from  the  spreading  ground.  Hand 
carrying  or  the  use  of  a  horse  and  wagon  are  generally  less  eco- 
nomical and  sanitary.  Miniature  steel  railroad  tracks  with  either 
steel  or  wooden  ties  are  the  most  substantial  and  permanent,  although 
wooden  rails,  if  faced  with  strap  iron  or  angle  iron,  are  satisfactory. 
Such  tracks  may  be  either  permanently  installed  or  portable  but  in 
either  case  should  be  smoothly  laid  so  that  the  juice  in  the  cups  of 
freshly  sulfured  peaches  and  apricots  is  not  spilled  during  transporta- 
tion. The  arrangement  of  tracks  with  respect  to  the  dipping  or  cut- 
ting shed,  sulfur  houses,  dry-yard  and  dried  fruit  storage  space  should 
be  such  that  the  fruit  moves  forward  steadily  through  the  various 
operations  with  the  minimum  retracing  of  routes.  Empty  trays  and 
cars  should  be  returned  to  the  reloading  point  without  coming  in  con- 
tact with  loaded  cars.  The  amount  of  trackage  must  be  determined 
by  the  quantity  of  fruit  handled  daily  and  the  area  and  shape  of  the 
dry  yard. 


Fig.  5. — Turntable  for  changing  direction  of  tray  cars. 
(Cut  furnished  by  Anderson  Barngrover  Co.) 

The  usual  type  of  tray  car,  as  illustrated  in  fig.  4,  consists  of  a 
low  wooden  frame  about  3'  x  6',  supported  by  four  cast-iron  wheels 
on  steel  axles.  Such  cars  will  carry  from  20  to  25  3'  x  8'  trays  holding 
from  1000  pounds  of  apricots  to  2000  pounds  of  prunes.  In  order  to 
provide  the  necessary  flexibility  in  the  transportation  system  as  in 
moving  cars  in  and  out  of  sulfur  houses  and  to  various  parts  of  the 
dry  yard,  use  is  made  of  steel  or  wooden  transfer  cars  or  of  turn 
tables  sunk  below  the  standard  track  level  so  that  the  tray  cars  can 
be  run  on  them  for  movement  at  right  angles  to  their  previous  direction 
(see  figs,  4  and  5). 

Figure  6  shows  a  suitable  arrangement  for  a  2%  acre  dry-yard 
equipped  to  handle  cut  and  sulfured  as  well  as  dipped  fruits.  It  is  not 
expected  that  this  plan  will  fit  all  conditions  but  should  serve  as  a 
guide  in  planning  a  well  arranged  dry -yard. 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


23 


Space  for  dry  ma  pi 


<h-  s-ogu<je  Ttach ? 


C  uttino  Shed  and    Tab/es 

E^kCZI  CZI  EU  CD  CD 


Dr  y    yard  Sp< 


STm 


CD  CD  CD  CD  CD  CD 


y     yard    Spac 


Ground  plan  of  a 
\  Dry   yard- Approx.2%A 

This  yard  will  accomodate 
Qpprox.  So  acres,  of  orchard 
ot  5 areen  Tons  per- A 


Fresh  FruiT 
Spac. 


Prune  dippt 
and  qrader 


Fig.  6. — Ground  plan  of  a  dry-yard. 


w 


Cgj) 


© 


CUTTING  SHEDS 

While  small  quantities  of  fruit  are  frequently  cut  and  trayed 
under  the  shade  of  trees  adjacent  to  the  dry-yards,  the  use  of  an 
inexpensive  shed  is  generally  desirable,  not  only  to  protect  the  cutters 
and  the  fruit  during  preparation  but  to  serve  as  a  convenient  storage 
place  for  trays,  boxes  and  other  equipment  during  the  winter.  For 
most  orchards  an  open  shed,  with  a  tight  roof,  sufficiently  large  to 
accommodate  the  number  of  cutters  employed,  is  adequate.  It  should 
be  so  located  that  prevailing  winds  will  not  blow  fumes  from  the  sulfur 
houses  toward  it  and  may  be  walled  on  one  or  more  sides  to  give  pro- 
tection from  wind-blown  dust  or  sulfur  fumes.  Ample  light  and 
ventilation  are  necessary  for  efficient  work  by  the  cutters. 

The  fruit  is  unloaded  at  one  end  or  side  of  the  shed  and  carried 
to  the  cutting  tables  as  required.  An  inexpensive  and  convenient  cut- 
ting table,  designed  to  hold  one  3'  x  8'  tray  or  several  smaller  trays 
and  provided  with  brackets  on  both  sides  to  hold  boxes  of  fruit  for 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


cutting,  is  shown  in  fig.  7.  The  track  for  loading  cars  should  be 
adjacent  to  the  rows  of  tables  so  that  each  tray  as  it  is  filled  may  be 
placed  on  a  car  and  replaced  by  an  empty  tray.     The  floor  of  large 

-7- 

VI an  for  C aft i no  Table 


TopVi 


ew 


/ 


h-6-^ 


Side  V/ew 


8 


->~«^-h 


"kw1  W.M IWA1^ 


It 


■Alh 


h 
u 


End  l//ew 


Fig.  7. — Plan  for  fruit  cutting  table. 

sheds  where  much  trucking  is  necessary  should  be  of  wood  or  concrete 
but  in  small  sheds  the  natural  ground  may  be  used  if  sprinkled  daily 
to  prevent  dust  rising.    The  comfort  afforded  cutters  by  stools  results 


Bull.  3S8] 


PRINCIPLES    OF   SUN-DRYING   FRUIT 


25 


in  greater  efficiency.  Sharp  knives  and  small  pans  or  boxes  for  the 
collection  of  pits  and  spoiled  fruit  are  necessary  to  secure  cleanly  cut 
fruit.  Water,  soap  and  paper  towels  should  be  provided  so  that  the 
cutters  may  frequently  wash  their  hands  and  knives.  Sanitary  toilets 
and  drinking  fountains  are  sanitary  requirements.  A  small  supply 
of  iodine,  bandages  and  adhesive  tape  is  necessary  "first-aid"  equip- 
ment for  cuts  or  scratches.     Cards  on  which  are  marked  or  punched 


H±z 


Fig.  8. — Dump  basket,  prune  or  grape  dipper,  with  lye  tank  and  furnace. 
(Cut  furnished  by  Anderson  Barngrover  Co.) 

the  number  of  boxes  of  fruit  cut  by  each  person  daily  furnish  a  simple 
and  invaluable  record  of  the  payment  due  to  cutters  and  of  the  amount 
of  fruit  handled.  In  fairness  to  the  cutters  and  as  a  record  of  the 
amount  of  fruit  picked  and  cut  each  box  should  be  made  up  to  the 
same  net  weight  before  cutting. 


DIPPEES 


Basket  dippers  are  used  for  both  grapes  and  prunes.  The  simplest 
type  illustrated  in  fig.  8,  consists  of  an  oblong  basket  with  a  rounded 
bottom  of  perforated  sheet  metal  or  wire  screen.    This  basket  is  hinged 


26  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

to  one  edge  of  the  lye  tank  so  that  after  immersion  the  basket  may  be 
raised  by  a  lever,  the  fruit  drained  and  emptied  directly  on  to  the  tray 
or  into  a  small  bin  or  a  shaker  which  in  turn  discharges  on  to  the 
trays.  Another  type,  known  in  Sutter  County  as  the  "Merry-go- 
round,"  and  used  especially  for  Sultanina  (Thompson  Seedless)  types, 
suspends  the  basket  from  an  over-head  counterbalanced  beam  which  is 
fastened  to  a  pivoted  upright.  The  fruit  is  emptied  into  the  basket  at 
one  point,  the  basket  swung  over  the  lye  tank  and  submerged,  removed 
from  the  lye  tank  and  swung  to  the  other  side  for  discharging  the 
grapes  on  to  the  trays.  If  two  opposite  baskets  are  used,  loading  and 
unloading  may  proceed  simultaneously,  the  baskets  describing  a  com- 
plete circle  for  each  load.  Continuous  automatic  dippers  consisting 
either  of  an  endless  draper  or  a  series  of  baskets  supported  by  two 
endless  chains,  are  used  in  a  few  of  the  larger  grape  dry-yards. 

Rotary  Dippers  are  used  only  for  prunes  and  consist  of  a  rotating 
perforated  metal  cylinder  the  lower  third  of  which  is  submerged  in 
the  lye  solution.  The  prunes  are  emptied  in  at  one  side  and,  by  means 
of  vanes  set  at  the  proper  angle  on  the  inner  walls  of  the  drum,  are 
carried  down  through  the  lye  solution  and  discharged  at  the  opposite 
side.  These  dippers,  illustrated  in  fig.  9,  are  automatic  and  continuous 
and  have  the  greatest  capacity.  They  are  operated  by  a  gas  engine 
or  electric  motor  and  the  speed  of  rotation  can  be  varied  to  regulate 
the  time  of  immersion.  Rotary  dippers  can  be  provided  with  a  vibrat- 
ing screen  on  which  the  prunes  are  emptied  for  separation  of  dirt  and 
leaves,  before  entering  the  dipper.  This  results  in  cleaner  fruit  and 
prevents  the  lye  solution  becoming  dirty  so  rapidly. 

Lye  tanks  have  a  capacity  of  from  100  to  200  gallons  and  are 
mounted  in  a  rectangular  brick  furnace.  Wood  is  used  by  some  as  a 
source  of  fuel  but  the  majority  use  some  of  the  forms  of  oil  burner 
because  they  can  be  made  to  maintain  a  constant  temperature  with  very 
little  attention.  The  less  expensive  natural  draft  burners  require  a 
refined  oil  such  as  kerosene  while  forced  draft  burners  utilize  the  less 
expensive  stove  oil  or  even  crude  oil.  In  a  few  places  the  lye  tank  is 
heated  by  steam  coils  but  this  system  is  not  recommended  unless  a 
steam  boiler  is  required  for  other  purposes. 

LYE 

The  lye  used  in  dipping  is  sodium  hydroxide  or  "caustic  soda." 
The  commercial  product,  granulated  or  in  flakes,  contains  95  per  cent 
or  more  of  sodium  hydroxide,  the  active  ingredient.  It  should  be  kept 
in  tight  metal  containers  to  prevent  absorption  of  moisture  from  the 
air.     Some  brands  of  "lye"  consist  partly  of  sodium  carbonate  or 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


27 


28 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


"sal  soda,"  a  compound  which  is  not  so  strongly  alkaline  as  sodium 
hydroxide  but  gives  equally  satisfactory  results  if  used  in  sufficient 
strength.  The  stronger  sodium  hydroxide  is  preferred  for  prunes, 
while  the  milder  sodium  carbonate  either  alone  or  in  combination  with 
sodium  hydroxide  is  largely  used  on  the  more  easily  affected  Sultanina 
(Thompson  Seedless)  grapes.  Sodium  bicarbonate  or  "baking  soda" 
is  another  and  much  weaker  alkaline  salt  which  is  used  in  the  dipping 
of  "oil  bleached"  raisins. 


Fig.  10. — Hand-operated  basket  prune  dipper,  with  lye  tank  and  furnace, 
connected  to  power-driven  grader.  Tray  supports  in  foreground.  (Cut  furnished 
by  Anderson  Barngrover  Co.) 

GRADERS 

Graders  are  used  in  conjunction  with  most  of  the  larger  prune 
dippers.  The  dipped  prunes  are  separated  into  two  or  three  sizes  by 
passing  over  vibrating  screens  which  can  be  changed  to  suit  the  sizes 
desired.  This  so-called  "green  grading"  is  valuable  in  securing  more 
even  drying  by  placing  the  small  and  large  prunes  on  separate  trays. 
If  grading  is  not  done,  the  small  prunes  may  be  over  dried  when  the 
large  ones  on  the  same  tray  are  still  too  moist.  This  necessitates  extra 
trays  and  sorting.    A  small  grader  is  illustrated  in  fig.  10. 


BULL.  388]  PRINCIPLES    OF   SUN-DRYING   FRUIT  29 

Needle  hoards  are  often  incorporated  with  graders.  They  consist  of 
a  flat  vibrating  board  or  sometimes  a  rotating  cylinder,  each  studded 
with  short  sharp  needles,  and  are  frequently  used  to  supplement  the 
dipping  of  prunes.  When  prunes  of  varying  degrees  of  maturity  are 
dipped  together,  the  skins  of  those  which  are  not  checked  by  the  lye 
solution  are  at  least  punctured  by  the  needles,  providing  apertures  for 
the  rapid  and  even  evaporation  of  moisture. 

TEAYS 

The  most  common  sizes  of  trays  used  are  the  2'  x  3',  3'  x  6'  and 
3'  x  8',  illustrated  in  fig.  11.  Other  sizes  have  no  special  advantages 
and  are  seldom  used.  The  2'  x  3'  tray  is  referred  to  as  the  raisin  tray 
because  it  is  universally  used  in  the  natural  drying  of  raisins  in  the 
vineyard.  In  the  raisin  sections  it  is  also  used  for  peaches,  apricots 
and  figs.  The  3'  x  6'  tray  is  used  for  peaches,  apricots,  figs  and  dipped 
grapes,  especially  seedless.  It  is  also  used  for  prunes  and  pears 
although  in  Lake  County  a  special  tray,  2%'  x  7'  is  preferred  for 
pears.  The  3'  x  8'  tray  is  preeminently  the  prune  tray  but  is  also  used 
for  peaches,  pears  and  apricots.  Table  6  gives  the  usual  specifications, 
capacities  and  costs  of  the  standard  trays.  It  must  be  borne  in  mind 
that  the  weight  of  fruit  which  can  be  spread  in  a  single  layer  on  one 
square  foot  of  tray  surface  varies  considerably  with  the  size  of  the 
individual  pieces  of  fruit.  Unless  below  average  size,  apricots  can  be 
spread  at  the  rate  of  two  pounds  and  peaches  three  pounds  per  square 
foot.  Pears  and  prunes  vary  from  three  to  four  pounds  per  square 
foot  but  not  usually  less  than  three  and  one-half  pounds.  Muscat 
grapes  do  not  fall  below  three  and  one-half  pounds  per  square  foot 
but  seedless  grapes  are  usually  spread  about  three  pounds  per  square 
foot. 

The  number  of  trays  required  to  sun-dry  a  given  tonnage  of  fruit 
during  the  season  varies  greatly  with  the  rapidity  with  which  the  fruit 
ripens  and  drys.  Prune  and  raisin  trays  are  generally  used  but  once 
each  season  and  it  is  therefore  necessary  to  have  sufficient  trays  to 
spread  the  entire  crop.  Trays  for  peaches  and  apricots  are  generally 
used  two  or  three  times  during  the  season  and  the  number  required 
is  proportionately  less.  In  estimating  the  number  of  trays  required  to 
dry  the  fruit  from  a  given  acreage,  the  tonnage  of  fruit  per  acre 
becomes  another  factor  of  variation.  Table  7  gives  the  approximate 
number  of  standard  trays  required  to  dry  various  fruits.  Such  figures 
are  subject  to  great  variation  but  the  limits  stated  in  Table  7,  cover 
most  cases. 


30 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 


SUWAQD  tyPLS 
OF  tWlC  OJAYS 

Scale  :-  *m.=  1ft. 


1 

'                              ' 

1                   1 

1 

1 

! 

I 

i .r-       -i 

J 


MATERIAL  FOR    3'*  6'  TRAY 


2.  Pieces 
2.        •' 
3       - 
16      " 


1i"»  12"-3iir 

r-  i8r"«  8' 


xr= 1 1  i= 

i — """ —  |  I  i  = 

-u 1 1  i, 

=i  j —  i- 


MATLR1AL   FOR    5*6'  TRAY 
%  P.eces S"*lf*6' 


MATERIAL  FOR    £»  3'  TRAY 


2  Pieces - 
X  "  - 
5  »  - 
1         »      - 


l"'iV'o' 

8'     6*0 
/6  "    11  "  Z 


Fig.  11. — Standard  types  of  fruit  trays. 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


31 


TABLE  6 
Specifications,  Capacities  and  Costs  of  Standard  Field  Trays 


Standard  specifications 

T  x  3'  Trays 

3'  x  6'  Trays 

3'  x  8'  Trays 

End  cleats 

2-^"xlM"x3' 
2-^"x  y8"x3' 

2-  %"xi%'xe' 

3-  ^"xlM'W 
12-  i4"x5M"x3' 

18' 

30-36 
40-50 
54-66 
45-60 
54-72 
54-72 

$.73 
$.78 

2-WxWx34M" 
2-  K"xlK"x8' 

Side  cleats 

Clinch  cleats 

3-  ^"xlM"x8' 

Bottom  boards 

5-^"x5M"x2' 

1-^"x7K"x2' 

6' 

10-12 
13-17 
18-22 
15-20 
18-24 
18-24 

$.17 
$.20 

16-  %"x5%"x3' 
24' 

Gross  area  in  sq.  ft 

Average  capacity  in  lbs.: 

Apricots 

Figs 

40-48 
53-67 

Grapes 

72-88 

Peaches 

Pears 

60-80 
72-96 

Prunes 

72-96 

Approximate  cost: 

[j|  In  shook 

Made  up 

$.90 
$1.00 

TABLE  7 
Number  of  Trays  Kequired  for  Sun-Drying* 


Apricots 

Figs 

Grapes: 

Muscat.... 

Sultanina 

Peaches 

Pears 

Prunes 


2'  x  3'  Trays 


Per  ton         Per  acre 


30-45 
15-20 

90-100 
110-120 
35-45 
40-80 
44-60 


150-500 
30-40 

315-350 
520-570 
260-340 
200-400 
220-760 


3'  x  6'  Trays 


Per  ton         Per  acre 


10-15 

5-7 

30-33 
37-40 
12-15 
13-27 
15-20 


50-166 
10-13 

105-117 

173-190 

87-113 

65-130 

73-253 


3'  x  8'  Trays 


Per  ton         Per  acre 


8-11 
4-5 

23-25 
28-30 
9-11 
10-20 
11-15 


38-125 
8-10 

80-88 
130-143 
65-85 
50-100 
55-190 


*  Calculated  from  observations  on  seasonal  tray  requirements  for  given  tonnages  and  acreages  of  fruit . 

Pine  is  the  most  common  kind  of  wood  used  for  trays.  Trays  with 
spruce  frames  and  pine  bottoms  are  considered  by  some  to  be  more 
sturdy  and  longer  lived.  Redwood  is  used  in  some  sections  because 
of  its  lower  cost.  Redwood  trays,  especially  when  new,  have  been 
known  to  stain  moist  light  colored  fruits  such  as  peaches,  pears  and 
apricots  but  are  satisfactory  for  prunes.  In  constructing  trays  the 
rougher  side  of  the  bottom  boards  should  be  up  because  dried  fruit 


32  •         UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

sticks  less  and  is  more  easily  removed  from  rough  than  smooth  sur- 
faces. Heavy  wrapping  paper  obtainable  in  bundles  of  2  reams  or  960 
sheets  is  used  for  drying  raisins  in  the  vineyard  when  wooden  trays 
are  unavailable.  Paper  trays  are  less  suitable  because  raisins  can  not 
be  properly  turned  or  stacked  on  such  trays  and  in  case  of  rain  may 
result  in  the  loss  of  raisins  because  the  wet  paper  can  not  be  handled. 
Furthermore,  paper  trays  hold  less  grapes,  more  are  spilled  on  the 
ground  and  more  dirt  incorporated  with  the  raisins.  Although  lower 
in  first  cost  (about  1  cent  each),  paper  trays  must  be  replaced  yearly 
and  are,  therefore,  if  we  consider  decrease  of  quality  and  losses  from 
rain  damage,  more  expensive  in  the  long  run  than  permanent  wooden 
trays. 

Clean  trays  are  necessary  for  the  production  of  clean  dried  fruit. 
If  trays  become  dusty,  sticky  or  moldy  they  should  not  be  used  until 
they  have  been  washed  and  dried.  If  properly  handled  such  washing  is 
generally  necessary  only  at  the  close  of  each  season.  The  use  of  a  stiff 
bristle  or  wire  brush  will  remove  all  dirt  after  it  has  been  softened  by 
immersing  the  tray  in  a  hot  solution  containing  sal  soda,  After 
rinsing,  the  trays  should  be  sulfured  and  thoroughly  dried  to  prevent 
molding  during  storage.  It  is  preferable  to  store  trays  in  some  sort 
of  building  or  shelter  which  keeps  the  trays  clean  and  dry  and  by 
protecting  them  from  the  weather  lengthens  their  useful  life. 


SULFUR  HOUSES 

Many  types  and  sizes  of  sulfur  houses,  varying  in  their  cost  and 
efficiency,  are  in  use.  The  simplest  and  cheapest  type  is  known  as  the 
sulfuring  "hood"  and  consists  of  a  light  wooden  framework  covered 
with  building  or  roofing  paper  (see  fig.  12).  It  is  open  at  the  bottom 
and  of  such  a  size  that  two  men  can  lift  it  up  by  the  handles  and  place 
it  over  a  stack  of  trays  on  the  ground.  The  sulfur  is  burned  in  a  hole 
in  the  ground  or  preferably  in  a  pan  or  bucket  set  on  the  ground  inside 
one  end  of  the  hood  which  should  be  made  at  least  a  foot  longer  than 
the  stack  of  trays.  Earth  is  shoveled  against  the  bottom  of  the  hood 
to  prevent  escape  of  sulfur  fumes.  Such  hoods  are  highly  inflammable, 
not  very  tight,  and  their  useful  life  is  limited  to  a  few  seasons.  Their 
use  is  not  recommended  except  in  emergencies  or  for  very  small  scale 
operations. 

The  most  common  sulfur  house  is  built  of  wood  made  as  tight  as 
possible  either  by  the  use  of  tongue  and  groove  lumber  or  by  common 
boards  lined  with  building  or  roofing  paper.     A  tight  fitting  door  at 


Bull.  388] 


PRINCIPLES    OF   SUN-DRYING   FRUIT 


33 


one  end  permits  the  entrance  of  a  truck  of  trays  which  is  rolled  into 
the  house  on  tracks.  Houses  of  concrete,  brick  or  hollow  tile  are 
always  tight  and  fire-proof  (see  fig.  13)  but  are  not  recommended  for 
the  efficient  sulfuring  of  fruit  with  the  minimum  amount  of  sulfur 
because  of  the  retarding  influence  of  the  cold  air  resulting  from  the 
resistance  of  these  materials  to  heat  penetration.  Heavy  beveled  doors 
with  locks  of  refrigerator  type  are  the  best. 


Top  V/eur 


Src/e  V/eW 


Q  a /loon    Hood 

/"x<?"  Wooden  Frame  Covered 
Wrffl     3  P/y   Budd,„a    PaPer. 


fnd  Viet* 


< —  >B"-i 

L_^__^ 

1                  v«l 

i 

1 J. 

\ —  -i-l -! 

.1 

SO 

1 

Fig.  12. — Balloon  hood  sulfur  box. 


For  efficiency  and  economy  in  sulfuring,  the  main  essentials  of 
sulfur  house  construction  are : 

1.  Tight  construction  to  prevent  leakage  of  sulfur  fumes. 

2.  Materials  of  construction  which  permit  warming  the  interior  by 
penetration  of  solar  heat. 

3.  Adequate  space  and  protection  for  the  sulfur  burning  equipment 
to  minimize  fire  hazard. 

Recent  investigations  by  R.  S.  Hiltner,  Technologist  of  the  Dried 
Fruit  Association  of  California  indicate  that  a  sulfur  house  built  of 
flat  sheet  iron  painted  outside  and  inside  with  black  asphalt  paint  to 
resist  rust  and  corrosion  fulfills  the  above  requirements. 


34 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


35 


Common  sulfur  houses  as  illustrated  in  figs.  14  and  15,  are  usually 
a  little  over  3  feet  wide  and  6  to  7  feet  high  inside.  The  length  should 
be  about  2  feet  more  than  that  of  the  car  of  trays,  to  provide  space 
for  burning  sulfur.    A  number  of  houses  sufficient  to  accommodate  the 


l*£n£ai 


■-L-.'iiV 


JV- 


Fig.  14. — Typical  sulfur  houses  with  counterpoised  door  hinged  at  top. 
Note  transfer  and  tray  cars. 


Fig.  15. — Typical  battery  of  wooden  sulfur  houses,  each  with  capacity  of 
two  cars.     Note  sliding  doors  and  counterweights. 

daily  output  of  the  cutting  shed  are  arranged  in  a  row  with  a  track 
and  transfer  car  along  the  front  to  facilitate  entrance  of  tray  cars  into 
each  house.  In  large  dry  yards  the  houses  are  often  built  long  enough 
or  wide  enough  to  hold  two  cars. 


36 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


H h--t— 4- 


Certter 


hr?e 


of  hoys 


V 


TOP    VIEW 


Root 


k//fur    dioxide  e$cap//?Q. 

ype  car?  be  easily 
iaker?  apart  at 
f/p/b  Jo/r?f. 


Fig.  16. — Metal  sulfur-burning  stove  and  distributing  flue  inside  a  tight 
sulfur  house.     (Courtesy  of  Dried  Fruit  Association  of  California.) 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


37 


Rear  Yval/ 


Grour?c/  line—^ 
Pi  pi 

Fig.  16A — Concrete  sulfur-burning  stove  and  distributing  flue  outside  a  tight 
sulfur  house.     (Courtesy  of  Dried  Fruit  Association  of  California.) 


38  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

While  the  sulfur  can  be  burned  in  a  small  pit  in  the  ground,  a 
better  practice  is  to  use  a  clean  pan  or  bucket  placed  either  on  the  floor 
inside  the  door  or  by  means  of  a  small  opening  for  this  purpose  in  the 
rear  of  the  house.  Such  containers  afford  easy  measurement  of  the 
sulfur  and  insure  complete  combustion  without  waste.  Where  the 
minimum  necessary  quantity  of  sulfur  is  used,  it  is  essential  that  com- 
plete combustion  of  the  sulfur  and  uniform  distribution  of  the  result- 
ing gas  throughout  the  house  be  secured.  A  sulfur  stove,  preferably  of 
brick  or  concrete,  with  a  distributing  flue  as  illustrated  in  fig.  16,  has 
been  found  to  cause  complete  combustion  and  distribution  of  the 
sulfur  fumes. 

If  such  stoves  are  used,  it  is  unnecessary  to  provide  openings  in  the 
house  for  admission  of  additional  air  because,  even  if  the  sulfur  house 
be  hermetically  sealed,  it  contains  sufficient  oxygen  to  burn  at  least 
two  pounds  of  sulfur  per  ton  of  green  fruit. 

The  number  of  sulfur  houses  required  is  dependent  on  the  acre- 
yield  and  the  rate  at  which  the  fruit  is  picked  and  cut.  With  peaches 
and  apricots,  each  sulfur  house  will  care  for  from  four  to  ten  acres 
of  orchard  during  the  season,  an  average  being  one  house  to  six  acres. 
Each  house  can  rarely  be  used  for  more  than  two  trucks  or  from  one 
to  two  tons  of  fruit  daily.  Since  pears  are  normally  sulfured  24  hours 
or  longer,  the  number  of  sulfur  houses  required  will  be  2  or  3  times 
that  required  for  peaches  or  apricots. 


SULFUR 

Any  kind  or  brand  of  sulfur  which  is  free  from  arsenic  and  will 
burn  readily  can  be  used  in  fruit  drying.  The  kind  most  commonly 
used  is  known  as  sublimed  flowers  of  sulfur.  The  light  fluffy  texture 
of  this  refined  sulfur  is  such  that  it  is  readily  ignited  by  a  match  or  a 
bit  of  burning  paper  and  burns  steadily  and  completely  without 
further  attention.  A  cheaper  form  of  sulfur  is  a  ground  or  lump 
crude  sulfur  which  is  sufficiently  pure  for  use  on  fruit.  However, 
the  physical  condition  of  this  sulfur  is  such  as  to  require  special  sulfur 
burning  stoves  or  pans  to  insure  its  combustion.  These  stoves  or  sets 
of  superposed  pans  retain  enough  of  the  heat  generated  by  the  burning 
sulfur  so  that  the  sulfur  burns  continuously  until  all  is  consumed. 
While  the  use  of  the  cheaper  crude  sulfur  should  result  in  a  slight 
saving,  most  growers  prefer  the  flowers  of  sulfur  because  it  obviates 
the  necessity  of  special  stoves  or  pans  and  of  frequent  attention  to  the 
sulfur  fires.     All  sulfur  should  be  kept  in  a  dry  place  to  prevent 


Bull.  388]  PRINCIPLES   OF   SUN-DRYING   FRUIT  39 

absorption  of  moisture  which  would  interfere  with  combustion.  The 
admixture  of  not  over  5  per  cent  of  powdered  sodium  or  potassium 
nitrate  (saltpeter)  (one  pound  to  20  pounds  of  sulfur)  insures  com- 
plete combustion  even  under  adverse  conditions. 

SWEAT  BOXES  AND  BINS 

Various  methods  are  in  use  for  temporary  storage  of  the  dried  fruit 
before  delivery  to  the  packing  house.  Some  fruits,  especially  prunes, 
and  to  a  considerable  extent  cut  fruits  are  concentrated  in  large  piles 
on  a  wooden  or  concrete  floor  for  storage  and  equalization.  The  dried 
fruit  may  either  be  emptied  into  lug  boxes  in  the  dry -yard  for  transfer 
to  the  storage  building  or  the  trays  of  dried  fruit  can  be  stacked  on 
cars  and  brought  directly  to  the  storage  place  for  unloading.  If  large 
tonnages  must  be  stored  on  a  restricted  floor  area  it  becomes  necessary 
to  construct  wooden  bins,  at  least  one  wall  of  each  being  constructed  of 
heavy  removable  boards  to  facilitate  emptying.  The  construction  of 
such  bins  is  best  learned  by  visiting  a  modern  packing  house.  In 
calculating  the  capacity  of  dried  fruit  bins,  the  factors  given  in  Table 
8  will  be  found  helpful. 

TABLE  8 
Capacity  Factors  for  Dried  Fruit  Bins 

Average  pounds 
Fruit  per  cubic  foot 

Apricots 54 

Figs,  white 53 

Figs,  black 55 

Peaches 49 

Pears 56 

Prunes 59 

The  common  method  of  transferring  such  fruits  from  the  growers ' 
bins  to  the  packing  house  is  in  sacks,  usually  used  grain  sacks.  A  better 
method  is  to  use  lug  or  sweat  boxes  because  sacks  not  only  require 
sewing  but  also  cause  the  fruit  to  accumulate  dirt.  Flat  cut  fruits  such 
as  peaches  and  apricots  become  more  curled  up  when  sacked.  This 
results  in  a  reduction  of  the  percentages  of  the  larger  sizes  when 
graded  and  for  this  reason  box  delivery  is  preferable. 

Raisins  and  white  figs  are  almost  invariably  collected  in  sweat  boxes 
after  drying  in  the  vineyard  or  dry-yard.  These  boxes  are  strongly 
built  with  ends  of  l1/4"  and  sides  and  bottom  of  %"  pine,  reinforced 
by  corner  posts.    They  are  about  38y2"  x  26%"  by  7%"  deep  and  cost 


40  UNIVERSITY    OF    CALIFORNIA— EXPERIMENT    STATION 

about  $1.25  each.  The  capacity  varies  from  100  to  200  pounds  of 
dried  fruit.  They  are  used  both  to  store  and  equalize  the  fruit  after 
drying  as  well  as  containers  in  which  to  deliver  to  the  packing  house. 
Lug  boxes  are  less  satisfactory  because  of  their  smaller  capacity  but 
can  be  used,  if  available  in  sufficient  numbers,  to  reduce  the  investment 
in  equipment. 


PRACTICES  OF  SUN-DRYING  FRUIT 
PICKING  METHODS 

Apricots  and  peaches  should  be  picked  from  the  tree  when  they  have 
a  uniform  ripe  yellow  color,  when  they  have  begun  to  soften  but  are 
still  reasonably  firm  and  when  they  can  be  easily  cut  with  a  sharp 
knife  and  yet  retain  their  shape.  In  order  to  obtain  only  well-ripened 
fruit  it  is  necessary  to  pick  over  the  orchard  from  two  to  four  times 
in  a  season.  The  number  of  pickers  required  per  acre  of  orchard 
averages  one  to  four  for  peaches  and  one  to  two  for  apricots.  The 
average  adult  will  pick  one  thousand  pounds  of  apricots  or  two 
thousand  pounds  of  peaches  a  day.  If  knocked  to  the  ground  for 
gathering,  these  figures  will  be  considerably  increased  but  the  fruit 
will  be  bruised  and  uneven  in  ripeness.  The  average  cost  of  hand 
picking  is  three  dollars  and  fifty  cents  per  ton  of  peaches  and  seven 
dollars  per  ton  of  apricots. 

Figs  drop  naturally  to  the  ground  when  mature.  The  ground 
should  be  smoothed,  to  keep  the  figs  cleaner  and  easier  to  gather.  The 
trees  may  be  lightly  shaken  but  the  fruit  should  never  be  knocked  off 
with  poles.  The  fallen  figs  should  be  gathered  frequently  as  exposure 
causes  them  to  become  sunburned,  dirty  and  infested  with  insects. 
In  practice,  however,  it  is  rarely  possible  to  cover  the  orchard  more 
than  once  or  twice  a  week. 

A  simple  and  economical  method  is  used  with  Mission  figs  in  the 
Winters  district.  The  fallen  figs  are  picked  directly  into  sacks,  which, 
when  one-third  to  one-half  full,  are  tied  and  flattened  out  on  the 
ground  under  the  tree  half  way  out  from  the  trunk.  The  sacks  are 
turned  every  two  or  three  days  until  the  figs  are  uniformly  dried  when 
several  sacks  are  condensed  for  hauling  to  storage  bins.  Very  uniform 
drying  results  in  dry  weather  but  the  figs  are  apt  to  become  excessively 
dirty  and  accumulate  lint  from  the  sack. 

The  entire  cost  of  picking  and  drying  by  this  method  is  about  $17 
per  dry  ton  and  requires  one  picker  to  each  two  acres. 


BULL.  388]  PRINCIPLES   OF   SUN-DRYING   FRUIT  41 

White  figs  picked  into  boxes  require  about  one  picker  to  each  eight 
acres,  at  the  rate  of  one  thousand  pounds  per  picker  daily.  The  cost 
of  picking  averages  ten  dollars  per  dry  ton. 

Pears  are  picked  from  the  tree  when  hard  ripe  and  still  green  in 
color  and  when  the  stem  separates  readily  from  the  spur.  It  is  neces- 
sary to  pick  over  the  orchard  two  or  three  times  in  order  to  secure 
pears  of  even  maturity.  Windfalls  should  be  gathered  frequently, 
preferably  daily.  In  some  orchards  a  layer  of  straw  is  spread  under 
each  tree  to  minimize  bruising  and  keep  the  pears  clean. 

Grading  and  Ripening  Pears. — When  received  at  the  preparation 
shed,  pears  should  be  graded  before  ripening  in  order  to  obtain  even- 
ness in  both  ripening  and  drying.  Grading  may  be  accomplished  by 
hand  or  by  special  pear  grading  machines,  the  latter  being  more  exact 
and  economical  for  large  plants.  Wormy,  sunburned,  bruised  or 
blemished  fruit  should  be  separated  as  it  not  only  ripens  faster  but 
makes  a  second  grade  dried  product.  The  sound  pears  are  graded 
into  from  three  to  five  sizes,  In  some  localities  the  medium  sizes  are 
reserved  for  fresh  shipment  or  canning.  The  various  grades  of  each 
day's  picking  are  stacked  in  separate  boxes  for  ripening,  which  requires 
from  five  to  ten  days.  During  this  time  the  pears  are  sorted  two  or 
three  times  to  remove  ripened  or  rotten  pears.  In  the  absence  of  suffi- 
cient boxes,  pears  may  be  ripened  in  shallow  bins  covered  with  a 
canvas  or  even  between  thick  layers  of  straw  under  the  shade  of  a 
tree  or  shed.  Such  methods,  however,  require  more  labor  and  result 
in  greater  loss  from  rotting.  Pears  are  ready  for  cutting  when  they 
have  acquired  a  uniform  yellow  color  and  full  pear  flavor,  when 
slightly  soft  to  thumb  pressure  yet  still  firm  and  not  over-ripe  or 
mushy. 

Prunes  are  always  picked  from  the  ground,  which  should  be  smooth 
and  free  from  vegetation  to  facilitate  clean  and  rapid  harvesting.  If 
prunes  remain  on  the  tree  after  reaching  maturity  it  becomes  necessary 
to  shake  the  trees  or  even  knock  the  fruit  off  with  poles  in  order  that 
the  crop  may  be  gathered  before  the  season  becomes  too  late  for  sun- 
drying. 

The  prune  orchard  is  picked  over  on  the  average  about  four  times, 
at  intervals  of  a  week  or  more.  The  final  picking  is  preceded  by  a 
thorough  shaking  or  knocking,  in  order  to  bring  down  all  the  remain- 
ing prunes.  An  average  crop  requires  one  picker  for  each  five  to  seven 
acres.  Adult  pickers  average  nearly  one  ton  a  day,  the  rate  of  pay 
varying  from  four  dollars  to  six  dollars  a  ton. 


42  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Grape  pickers  cut  the  stems  with  a  sharp  knife  and  spread  the 
bunches  directly  on  2'  x  3'  trays  holding- 18  to  22  pounds  each.  Before 
picking  begins,  trays  are  distributed  between  the  rows  and  a  ridge  of 
soil  thrown  up  against  the  south  side  of  the  east  and  west  rows.  The 
filled  trays  are  placed  against  this  ridge  and  are  thus  tilted  toward  the 
south  in  order  to  secure  the  maximum  effect  of  the  sunshine.  Pickers 
are  paid  from  two  and  one-half  to  five  cents  a  tray  according  to  the 
number  of  trays  of  grapes  per  unit  of  five  hundred  vines,  the  average 
being  three  and  one-half  cents  a  tray.  This  is  equivalent  to  a  cost  of 
three  dollars  to  three  dollars  and  a  half  per  ton  of  grapes.  Generally 
the  entire  crop  is  removed  at  one  picking. 

Grapes  which  are  dipped  and  sulfured  before  drying  are  picked 
into  boxes  and  hauled  to  a  dry -yard. 

Boxes  of  fruit  should  not  be  allowed  to  remain  in  the  orchard  for 
more  than  one  day  after  picking.  They  should  be  stacked  in  the 
shade  and  delivered  to  the  preparation  shed  as  promptly  as  possible 
in  order  that  preparation  and  drying  may  begin  while  the  fruit  is  in 
the  freshest  possible  condition.  This  is  especially  important  with  fruit 
which  has  been  bruised  in  falling  to  the  ground. 

WASHING 

While  not  the  general  practice,  washing  apricots  and  peaches  before 
cutting  increases  the  quality  of  the  dried  product  and  therefore  the 
price  obtained,  as  has  been  demonstrated  by  comparative  tests,  because 
the  fruit  is  cleaned  and  the  surface  left  moist  for  the  quick  and  uni- 
form action  of  sulfur  fumes.  This  is  especially  true  of  fruit  gathered 
from  the  ground  after  being  shaken  from  the  tree. 

The  simplest  method  of  washing  consists  in  emptying  the  fruit  from 
the  picking  boxes  into  slat  bottom  lug  boxes,  immersing  in  a  tank  of 
clean  water,  draining  and  using  these  boxes  as  service  boxes  to  supply 
fruit  to  the  cutters. 

CUTTING  AND  PITTING 

Apricots  and  peaches  are  cut  by  running  a  sharp  knife  around 
the  line  of  the  suture  so  that  the  knife  blade  returns  to  the  point 
where  the  cut  began.  The  two  neatly  cut  halves  are  then  separated, 
the  pit  picked  out,  and  the  two  halves  laid  immediately  on  to  a  clean 
tray  with  the  cut  surface  up.  The  fruit  should  not  be  cut  part  way 
around  and  then  torn  apart,  as  this  leaves  ragged  unattractive  edges. 
The  pieces  are  placed  close  together  to  utilize  the  maximum  capacity 
of  the  tray,  but  should  not  be  crowded  or  overlapped  as  this  causes 


BULL.  388]  PRINCIPLES   OF   SUN-DRYING   FRUIT  43 

the  juice  to  spill  out  of  the  pit  cavities  when  the  trays  are  handled 
after  sulfuring,  resulting  in  a  loss  of  weight  and  sticky  fruit  and  trays. 
In  order  to  keep  the  trays  and  fruit  clean,  uncut  fruit  should  not  be 
emptied  on  to  the  tray  but  should  be  removed  from  the  lug  box  as  it 
is  cut  and  the  pits  thrown  into  a  separate  box  or  pan  for  collection 
and  drying.  Overripe  fruit  which  will  make  "slabs"  is  preferably 
placed  on  separate  trays  so  as  to  simplify  culling  the  dried  product. 
Kotten  fruit  should  not  be  thrown  back  into  the  lug  box  or  with  the 
pits,  but  into  a  separate  receptacle. 

For  apricots,  an  average  of  one  cutter  to  each  acre  of  orchard  is 
required.  Cutters  are  paid  from  seven  to  twenty-five  cents  a  box, 
averaging  thirteen  cents,  the  rate  being  regulated  to  some  extent  by 
the  size  of  the  fruit  but  more  by  the  local  labor  supply  and  demand. 
One  person  will  cut  from  eight  hundred  to  two  thousand  pounds  daily, 
the  average  being  about  one  thousand  pounds.  The  cost  of  cutting 
ranges  from  $5  to  $8,  averaging  $6  a  ton.  Cutters  should  be  paid  at 
a  rate  per  box  which  permits  the  grower  to  insist  on  proper  cutting 
and  still  enables  cutters  to  earn  fair  wages.  Comparative  tests  have 
shown  that  improper  cutting  by  underpaid  cutters  results  in  a  greater 
loss  in  value  of  the  dried  product  than  the  apparent  saving  from 
reduced  cutting  costs. 

With  peaches,  one  cutter  for  each  2  to  5  acres  is  required.  Cutters 
are  paid  from  six  to  ten  cents  a  box  and  average  two  thousand  pounds 
a  day.    The  average  cost  of  cutting  peaches  is  $3.50  a  ton. 

Pears  are  cut  through  the  center  from  calyx  to  stem  and  the  stem  is 
pulled  out.  Worm  holes  should  be  trimmed  out  and  some  growers 
also  trim  out  the  calyx.  The  core  can  be  removed  from  each  half  by  a 
special  steel  loop  pear  corer.  This  gives  the  finest  product  but  adds  to 
the  cost  of  preparation  and  reduces  the  yield.  Cutters  are  paid  from 
ten  to  twenty  cents  per  box  of  50  to  60  pounds  net.  The  rate  varies 
according  to  the  locality,  the  size  of  the  pears  and  the  amount  of  trim- 
ming required.  An  experienced  person  can  cut  twenty  boxes  a  day. 
The  average  rate  in  1922  was  fifteen  cents  a  box,  equivalent  to  about  $5 
a  ton. 

DIPPING 

Prunes  should  be  dipped  in  a  hot  alkali  solution  as  soon  as  is  con- 
venient after  harvesting.  The  lye  solution  is  made  by  adding  1  pound 
of  lye  to  from  15  to  30  gallons  of  water,  usually  1  pound  to  20  gallons, 
which  is  equivalent  to  a  concentration  of  0.4  to  0.5  per  cent  lye.  The 
temperature  of  the  dip  varies,  with  different  operators,  from  lukewarm 
to  boiling,  but  comparative  experiments  have  shown  the  most  efficient 


44  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

temperature  to  be  200°  F.,  which  means  that  the  dip  should  be  main- 
tained close  to  the  boiling  point.  The  time  of  immersion  varies  from  a 
few  seconds  to  half  a  minute  but  if  the  temperature  and  lye  concen- 
tration are  correct,  from  5  to  15  seconds  is  ample.  The  strength  of  the 
solution  must  be  maintained  by  periodic  additions  of  lye  to  replace  that 
lost  mechanically  and  by  partial  neutralization  of  the  fruit  acid  and  at 
the  end  of  each  day's  dipping  the  lye  tank  should  be  drained  and  a 
fresh  solution  made  up  for  the  next  day. 


Fig.  17. — Effect  of  proper  lye  dipping  on  the  skins  of  prunes. 

Tough  skinned  varieties  such  as  the  Robe  de  Sergeant  require  a 
stronger  solution  and  longer  dip  than  more  tender  varieties,  such  as 
the  Imperial.  Frequent  examination  of  the  dipped  prunes  is  neces- 
sary to  regulate  the  strength  of  the  dip  and  time  of  immersion  in  order 
that  the  skins  of  the  majority  of  the  prunes  shall  develop  a  number  of 
minute  cracks  as  shown  in  fig.  17.  In  general  a  short  dip  in  a  fairly 
strong  lye  solution  close  to  the  boiling  point  gives  better  results  than 
a  long  dip  in  a  weak  or  lukewarm  lye.  If  the  prunes  are  so  tender 
as  to  become  partially  peeled  in  dipping,  it  is  necessary  to  reduce  the 
temperature  or  lye  concentration  or  both.  Some  growers  prefer  to 
dip  Imperials  merely  in  warm  water  to  which  little  or  no  lye  is  added. 

If  the  dip  can  not  be  adjusted  so  as  to  check  all  the  prunes,  the  use 
of  a  pricker  board  is  advantageous  because  the  skins  of  those  prunes 
not  checked  by  the  dip  are  at  least  perforated. 


BULL.  388]  PRINCIPLES    OF   SUN-DRYING   FRUIT  45 

Rinsing  after  dipping  is  not  practiced  by  all  growers  but  is 
generally  considered  advisable.  Rinsing  may  be  done  by  immersing 
the  prunes  in  a  second  tank  through  which  fresh  water  is  running  but 
preferably  by  passing  the  prunes  under  water  sprays. 

The  dipped  prunes,  either  graded  or  ungraded,  are  discharged  on  to 
the  trays  and  spread  close  together  one  layer  deep  only.  The  larger 
dipping  outfits  have  a  device  for  shaking  the  trays  to  minimize  the 
amount  of  labor  required  in  spreading.  The  filled  trays  are  then 
stacked  on  trucks  for  transfer  to  the  dry  yard. 

The  number  of  men  in  a  dipping  crew  varies  from  3  on  small  hand- 
power  dippers  to  as  high  as  7  on  the  largest  power  dippers;  averag- 
ing 5.  The  average  daily  capacity  for  a  typical  dipping  crew  was 
found  to  be  about  7000  pounds  per  man.  It  is  common  practice  for 
the  crew  to  dip  prunes  during  the  forenoon  and  to  spread  the  trayed 
prunes  and  do  other  dry-yard  work  in  the  afternoon.  Recently, 
mechanical  tray  stackers  installed  in  some  orchards  have  eliminated 
two  men  from  the  dipping  crew. 

The  average  operating  cost  of  dipping  and  spreading  prunes  on 
trays,  presented  in  Table  9,  is  based  on  exact  measurements  in  over 
20  dry-yards. 

TABLE  9 

Average  Cost  of  Dipping  and  Traying  Prunes 

Per  fresh  ton 

Lye,  1.3  pounds,  @  8j^c $  .11 

Power,  2.5  K.W.H.,  @  2c 05 

Fuel  oil,  2  gals.,  @  8c 16 

Labor,  1.95  man  hours,  @  40c 78 

Total SI.  10 

Grapes. — Sultaninas  and  Sultanas  are  dipped  before  drying  to 
produce  the  three  commercial  grades  known  as  :  Soda  Dipped,  Bleached 
and  Oil  Dipped.  For  the  first  two  grades  the  grapes  are  dipped  in 
much  the  same  way  as  that  just  described  for  prunes.  If  the  dip 
contains  1  pound  of  lye  to  every  10  to  20  gallons  of  water  and  is 
nearly  boiling,  satisfactory  dipping  is  obtained  in  five  seconds  or  less. 
Basket-type  dippers  must  be  used  and  the  clipped  grapes  should  be 
rinsed  before  traying.  Because  of  the  ease  with  which  the  skins  of 
Sultanina  grapes  can  be  checked  and  of  the  danger  of  over-dipping, 
most  growers  prefer  to  use  weaker  brands  of  lye  containing  as  much 
as  50  per  cent  sal  soda. 


46 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Soda-dipped  raisins  are  placed  directly  in  the  dry-yard  while 
bleached  raisins  are  sulfured  several  hours  after  dipping  and  before 
drying. 

Oil  Dipped  raisins  are  immersed  for  a  few  seconds  in  a  cold  solution 
of  30  pounds  of  bicarbonate  of  soda  (baking  soda)  and  1  pound  of 
lye  in  100  gallons  on  which  a  thin  film  of  olive  oil  is  floated.  The  water 
may  be  heated  to  hasten  the  solution  of  soda  if  necessary.  The  soda 
dissolves  the  waxy  bloom  of  the  grapes  and  causes  them  to  dry  more 
rapidly.  The  thin  film  of  olive  oil  with  which  the  grapes  become 
coated  gives  the  finished  raisins  a  glossy  lighter  brown  color  and  a 
softer  skin.  For  each  green  ton  of  grapes  dipped,  about  5  pounds  of 
sodium  bicarbonate  and  1  quart  of  olive  oil  are  consumed. 

Figs. — The  Adriatic  is  the  only  variety  of  fig  which  is  dipped.  A 
cold  brine  containing  from  5  to  20  pounds  of  salt  in  100  gallons  of 
water  is  the  most  common  dip,  although  some  growers  add  an  amount 
of  lime  equal  to  the  salt.  The  function  of  this  dip,  which  can  be 
applied  by  immersion  or  preferably  by  sprays,  is  to  cleanse  the  skin 
of  the  figs  and  leave  them  moist  to  facilitate  the  sulfuring  which 
follows.  Comparative  experiments  by  the  writers  have  shown  that 
plain  water  is  just  as  good  and  the  expense  for  salt  and  making  the 
brine  is  unnecessary. 

SULFUK1NG 

Sulfuring  methods  vary  considerably  with  variety  of  fruit,  con- 
struction of  sulfur  houses,  locality,  temperature,  etc.  The  figures  in 
Table  10,  represent  what  has  been  considered  common  practice. 

TABLE  10 
Average  Amounts  of  Sulfur  and  Times  for  Sulfuring  Fruits 


Fruit 


Hours  exposed 


Pounds  sulfur 
per  green  ton 


Cost  of  sulfur 
per  green  ton* 


Apricots 

Peaches 

Pears 

Grapes  (Seedless). 
Figs  (Adriatic) 


4 
5 
36 
4 
4 


7 
7 
12 
5 
3 


$.28 
.28 
.48 
.20 
.12 


*  At  4  cents  per  pound. 


The  quantities  of  sulfur  given  in  Table  10  are  many  times  the 
quantity  actually  absorbed  or  required  by  the  fruit.  This  is  because 
most  sulfur  houses  permit  a  steady  escape  of  sulfur  fumes  and  because 


Bull.  388]  PRINCIPLES    OF    SUN-DRYING    FRUIT  47 

many  operators  cause  the  fruit  to  absorb  as  much  sulfur  as  possible, 
incorrectly  believing  that  "if  a  drop  is  good,  a  bucketful  is  better." 

Recent  investigations  by  R.  S.  Hiltner,  Technologist  of  the  Dried 
Fruit  Association  of  California,  show  that  two  pounds  of  sulfur  per 
ton  of  peaches  or  apricots  is  ample  to  preserve  the  fruit  provided  this 
sulfur  is  completely  burned  and  the  fumes  distributed  in  a  tight  house. 
For  the  benefit  of  the  industry,  growers  should  make  their  sulfur 
houses  tight  and  restrict  the  amount  of  sulfur  burned  to  the  minimum 
required  for  color  preservation. 

In  general  it  may  be  said  that  the  best  results  are  obtained  by  the 
use  of  the  minimum  amount  of  sulfur  in  a  tight  warm  sulfur  house 
and  by  allowing  the  fruit  to  remain  in  the  house  for  12  to  24  hours 
after  the  sulfur  has  ceased  burning. 

Apricots  and  Peaches. — In  order  that  the  surface  of  cut  fruits  will 
be  moist  for  sulfuring,  each  tray  of  fruit  should  be  sprinkled  with 
water  or  a  weak  brine  (1  pound  of  salt  to  each  4  gallons  of  water)  as 
it  is  stacked.  Salt  aids  in  preventing  the  darkening  of  the  fruit  and 
reduces  the  amount  of  sulfur  required.  The  trays  should  be  alternately 
staggered  about  six  inches  at  the  ends  to  provide  easy  access  of  the 
fumes  to  the  fruit.  As  soon  as  a  stack  is  completed  it  should  be  imme- 
diately placed  in  the  house  for  sulfuring.  When  apricots  or  peaches 
are  sufficiently  sulfured,  the  pit  cavities  will  be  nearly  but  not  quite 
filled  with  juice,  the  skins  will  be  loosened  from  the  softened  flesh  and 
the  pieces  will  appear  uniformly  transluscent,  not  ' '  raw, ' '  either  when 
cut  transversely  or  viewed  toward  the  sun. 

Pears. — In  Lake  and  Mendocino  counties  where  the  highest  market 
grades  of  dried  pears  are  produced,  the  fruit  remains  in  the  sulfur 
house  from  24  to  72  hours,  the  sulfur  being  added  in  batches  of  2  to  4 
pounds  at  approximately  8-hour  intervals. 

In  other  parts  of  the  state  as  in  Contra  Costa  County,  pears  are 
usually  sulfured  less  than  24  hours  with  the  result  that  the  dried 
product,  although  of  good  flavor,  is  of  a  light  brown  color  and  brings 
a  lower  price. 

The  larger  and  greener  the  pears  the  longer  the  time  of  sulfuring. 
When  ready  for  drying  the  flesh  is  softened  throughout  as  if  cooked 
and  is  white  and  transluscent  while  the  skin  is  a  light  yellow.  In  order 
to  prevent  drying  of  the  cut  surface  during  sulfuring,  pools  or  pans 
of  water  are  used  for  maintaining  a  humid  atmosphere  within  the 
house. 

Grapes  and  Figs. — These  fruits  should  be  placed  in  the  sulfur 
fumes  while  still  moist  from  dipping  and  left  until  they  acquire  the 
uniform  light  yellow  color  desired. 


48 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 


DRYING 

Apricots  and  Peaches. — As  soon  as  sulfuring  is  complete  the  trays 
should  be  transferred  by  truck  to  the  dry -yard  and  spread  in  the  sun- 
shine, but  never  later  than  3  or  4  p.m.  The  trays  should  be  laid 
systematically  in  rows,  preferably  extending  north  and  south  and  at 
right  angles  to  the  tracks.  The  north  side  of  each  tray  should  rest 
on  the  south  edge  of  the  preceding  tray.  This  arrangement  economizes 
space  and  by  holding  all  but  one  edge  of  the  tray  off  the  ground  helps 
in  keeping  the  trays  clean  and  in  picking  them  up. 


Fig.  18. — Scraping  dried  apricots  into  lug  boxes.     Note  arrangement 
of  trays  for  stack  drying. 

The  fruit  should  remain  exposed  to  direct  sunshine  until  it  is  from 
a  quarter  to  half  dried  and  has  acquired  a  uniform  color.  This  will 
require  from  1  to  5  days  according  to  the  temperature  and  air  move- 
ment. The  trays  should  then  be  stacked  in  a  staggered  pile  with  the 
open  ends  in  the  direction  of  the  prevailing  winds.  After  2  to  6  days 
in  the  stack  the  fruit  will  be  dry  enough  for  storage.  The  total  drying 
time  varies  greatly  with  locality  and  weather  conditions  but  averages  7 
days  for  apricots  and  8  days  for  peaches. 

Before  the  dried  fruit  from  each  tray  is  scraped  into  lug  or  sweat 
boxes  (see  fig.  18),  discolored  pieces,  pits  or  other  foreign  matter 
should  be  picked  out.  This  important  culling  can  be  done  much  more 
efficiently  and  economically  at  this  point  than  at  any  later  time.  The 
dried  fruit  is  then  transferred  from  the  dry-yard  to  the  storage 
building. 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


49 


The  ratio  of  the  number  of  employees  required  for  operating  the 
cutting  shed  and  dry -yard,  exclusive  of  cutters,  to  the  bearing  acreage 
was  found  to  average  one  man  to  each  8  acres  of  apricots  or  each  12 
acres  of  peaches.  The  cost  of  this  labor  (at  40  cents  an  hour)  was 
found  to  average  $4.40  for  apricots  and  $4.60  for  peaches,  per 
green  ton. 

Prunes. — Prunes  are  placed  in  the  dry-yards  in  the  way  described 
for  apricots  and  peaches  but  the  trays  are  not  stacked  until  the  prunes 
are  about  three-fourths  dried  (see  fig.  19).  This  requires  from  5  to  10 
days  in  dry  weather.  During  this  period  large  prunes,  especially 
Imperials  and  Sugars,  should  be  stirred  by  hand  or  a  wooden  rake. 
By  turning  them  over  (see  fig.  20)  and  preventing  their  sticking  to 
the  tray,  drying  is  made  more  rapid  and  uniform,  and  loss  from  mold 
or  fermentation  minimized. 


Fig.  19. — A  large  prune  dry  yard. 

The  trays  are  then  stacked  for  completion  of  drying.  This  requires 
one  week  or  longer  according  to  weather  conditions.  Care  must  be 
taken  not  to  stack  prunes  until  they  are  at  least  three-fourths  dry  or 
they  may  spoil.  It  is  rarely  possible  to  properly  dry  prunes  in  less 
than  10  days  and  the  average  time  in  favorable  weather  is  two  weeks. 

Prunes  are  sufficiently  dry  when  the  flesh,  especially  that  around 
the  pit,  has  changed  to  a  thick  or  stiff  syrupy  condition  and  clings 
tight  to  the  pit.  When  a  handful  is  squeezed  hard,  the  prunes  should 
be  sufficiently  flexible  to  form  a  compact  mass  and  yet  not  soft  enough 
to  stick  together  when  the  pressure  is  released.  If  some  pits  are 
cracked  the  kernels  should  be  found  dry  and  shrunken. 

There  are  usually  some  prunes  which  do  not  dry  satisfactorily  and 
form  what  are  popularly  referred  to  as  ' '  bloaters, "  ' '  frogs, "  * '  choco- 


50 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


lates,"  etc.  These  are  the  result  either  of  inefficient  dipping,  or  of 
immaturity,  over-ripeness  or  partial  decay  of  the  prunes.  All  such 
defective  prunes  should  be  carefully  culled  out  either  during  drying 
or  before  the  trays  are  emptied  as  shown  in  fig.  21.  Failure  to  do  this 
will  seriously  lower  the  quality  of  the  entire  output. 


Fig.  20. — Turning  prunes  to  facilitate  drying. 


Pii 


-Sort 


(ln< 


The  average  number  of  dry-yard  employees,  exclusive  of  the  dip- 
ping crew,  was  found  to  be  one  man  to  each  15  acres  of  bearing  orchard. 
The  average  cost  of  all  dry-yard  labor,  exclusive  of  dipping,  was  found 
to  be  about  $2.40  a  green  ton  at  a  rate  of  40  cents  an  hour. 

In  case  of  rain  or  heavy  fog  during  the  drying  season,  the  trays 
must  all  be  closely  stacked  and  each  stack  covered  with  empty  trays, 
canvas  or  a  sheet  of  corrugated  iron  to  prevent  the  prunes  and  trays 
from  getting  wet.     If  the  prunes  are  already  partially  dried  and  the 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


51 


damp  weather  is  of  short  duration,  no  serious  damage  will  result.  As 
soon  as  the  air  is  comparatively  dry  again,  the  trays  should  be  spread 
on  the  ground  to  complete  the  drying.  If,  as  often  occurs  toward  the 
latter  part  of  the  prune  season,  weather  conditions  do  not  permit  of 
sun-drying,  recourse  must  be  had  to  dehydraters  which  at  a  tempera- 
ture of  165°  F.,  which  is  safe,  can  economically  complete  the  drying  of 
the  prunes  in  24  hours  or  less  without  danger  of  spoiling.  In  fact, 
the  economic  advantages  of  modern  dehydraters  for  prunes  have 
caused  many  growers  to  use  them  exclusively  in  preference  to  the 
hazardous  sun-drying. 


Pig.  22. — Drying  pears  in  Lake  County.     (Note  wooden  horses  for  tilting 
trays  toward  south  and  open  sheds  for  stack  drying.) 


Pears. — To  preserve  a  light  color,  pears  should  be  exposed  to  direct 
sunshine  for  only  one-half  to  two  days  after  sulfuring.  In  Lake  County 
the  north  end  of  each  tray  is  rested  on  wooden  horses  (about  1  to  IV2 
feet  high)  to  give  the  pears  the  maximum  sun  exposure  (see  fig.  22). 
The  trays  are  next  stacked  about  20  high,  staggered,  and  with  two 
1-inch  square  cross-bars  between  each  pair  of  trays  to  afford  ample 
air  circulation  for  drying.  Each  stack  should  be  covered  with  a  tray 
or  other  device  to  shade  the  top  tray  and  shed  rain.  In  Lake  County 
permanent  open-sided  sheds  are  used  to  stack  the  trays  under.  Two 
to  four  weeks  are  usually  required  to  complete  drying,  the  trays  being 
usually  restacked  two  or  more  times  to  permit  picking  out  culls  and 
pears  which  have  dried  sufficiently.  Rain  damage  is  rare  because  of 
the  high  sulfur  content  of  the  pears  and  the  protection  afforded  by 
stacking  and  sheds. 


52  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

Properly  dried  pears  should  be  light  colored  and  flat  with  little 
curling  of  the  cut  edges.  They  should  not  be  mushy  or  puffy  in  the 
center  but  of  a  uniform  texture  similar  to  soft  rubber. 

Figs. — Because  of  variations  in  the  moisture  content  of  figs  as 
usually  picked,  it  is  preferable  to  sort  out  and  tray  only  those  which 
are  relatively  soft  and  juicy  and  place  all  dried  or  nearly  dried  figs  in 
storage.  The  length  of  time  which  trays  of  soft  figs  should  be  exposed 
to  direct  sunshine  will  depend  on  their  moisture  content  and  the  tem- 
perature of  the  air.  In  very  warm  weather  the  trays  of  figs  need  not 
be  exposed  to  direct  sunshine  but  preferably  allowed  to  remain  stacked. 
In  cooler  weather  it  is  generally  necessary  to  expose  the  trays  for  two 
or  three  days  before  stacking,  but  care  should  be  taken  to  prevent 
rapid  or  excessive  drying,  which  results  in  a  tough  skin.  Stirring  the 
figs  on  the  trays  facilitates  even  drying. 

The  interior  of  a  properly  dried  fig  should  have  the  consistency  of 
a  very  thick  fruit  jam  or  butter  and  the  skin  should  be  soft  and 
pliable,  "like  a  kid  glove."  All  figs  which  are  split,  bird  pecked, 
moldy,  sour  or  otherwise  defective  should  be  culled  out  before  the 
figs  are  placed  in  sweat  boxes  for  delivery  to  the  packing  house. 

A  simple  and  fairly  satisfactory  method  of  drying  Mission  figs  in 
Yolo  County  is  described  on  page  40. 

Grapes. — There  are  two  general  methods  of  producing  raisins  from 
grapes : 

1.  Drying  untreated  grapes  on  trays  between  the  rows  in  the 
vineyard. 

2.  Drying  dipped  grapes,  with  or  without  sulfur  bleaching,  on 
trays  in  a  dry -yard. 

Practically  all  Muscat  raisins  and  the  greater  part  of  the  Sultanina 
(seedless)  raisins  are  dried  in  the  vineyard,  by  the  first  or  so-called 
"natural"  method. 

For  this  method,  before  the  grapes  are  ripe  for  picking,  a  ridge  is 
thrown  up  against  the  south  side  of  every  other  east  and  west  row  of 
vines,  with  a  plow  or  "V"  shaped  drag.  One  man  and  team  can 
cover  about  ten  acres  per  day.  This  operation  is  referred  to  as 
"V'ing.  At  this  time,  the  2'x3'  raisin  trays  are  distributed  in  the 
vineyard.  This  is  done  at  the  approximate  rate  of  3000  trays  a  day 
for  each  two  men  and  a  team.  The  pickers  cut  the  grapes  from  two 
adjacent  rows  simultaneously  and  spread  them  one  bunch  deep  directly 
on  the  trays  which  are  placed  so  that  one  end  rests  on  the  ridge  which 
tilts  the  trays  toward  the  south.  Care  should  be  taken  to  prevent  the 
trays  from  being  shaded  by  the  vines,  overhanging  leaves  being  clipped 
off  if  necessary. 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


53 


After  about  four  days  the  position  of  the  ends  of  the  trays  is  often 
reversed  in  order  to  secure  more  rapid  and  uniform  drying.  For  the 
same  reason,  when  the  grapes  on  the  upper  surface  of  the  bunches 
have  become  brown  in  color  and  partially  shrivelled,  the  contents  of 
the  trays  should  be  turned  over.  This  is  done  by  two  men  placing  an 
empty  tray  on  a  filled  one,  lifting  the  two  together  off  the  ground  and 
by  a  quick  turn  depositing  the  inverted  bunches  on  the  other  tray. 
Two  men  can  turn  about  3000  trays  a  day. 

When  all  the  grapes  have  developed  a  uniform  brown  color  and 
are  from  one-half  to  two-thirds  dry,  the  trays  are  stacked  in  piles 
20  or  more  trays  high. 

The  use  of  paper  trays  is  confined  principally  to  the  smaller,  more 
rapidly  drying  seedless  raisins.  The  ground  between  every  other  pair 
of  rows  should  be  smoothed  by  dragging,  the  papers  spread  on  this 
ground  and  held  down  by  a  bunch  of  grapes  until  they  are  filled. 
When  the  raisins  are  nearly  dry  enough  for  stacking,  the  sides  of  the 
papers  are  turned  in  and  the  papers  of  raisins  made  into  rolls  which 
are  then  stacked  like  logs  of  wood. 

When  the  grapes  are  sufficiently  dry  to  be  rolled  between  the 
fingers  without  exuding  moistore,  they  are  emptied  from  the  trays 
into  sweat  boxes  which  have  been  previously  distributed  through  the 
vineyard.  Since  each  sweat  box  will  hold  about  150  pounds,  13  boxes 
for  each  ton  of  raisins  will  be  required.  Two  men  are  able  to  box 
about  5  tons  a  day.  The  boxes  may  be  collected  at  once,  or  if  the 
weather  permits,  may  be  left  in  the  vineyard.  In  either  case,  the 
raisins  should  be  left  in  the  boxes  several  weeks  for  thorough  equaliza- 
tion of  moisture  before  delivery  to  the  packing  house.  After  the  trays 
are  emptied  they  must  be  collected  and  removed  from  the  vineyard. 

The  time  required  for  the  several  stages  in  the  drying  varies  con- 
siderably with  the  variety  and  size  of  the  grapes,  the  locality,  the  time 
of  year  and  the  climate.  The  figures  given  in  Table  11  will  serve  as 
an  approximate  guide. 


TABLE  11 

Approximate  Average  Time  Bequired  to  Dry  Eaisins 


Sultanina 

Muscat 

Turn  after 

Days 

7-8 

3-4 

7 

21 

Days 
10-12 

Stack  after 

5-7 

Box  after                       

7 

Deliver  after 

21 

54  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

The  production  of  dried  currants  from  the  Black  Corinth,  a  very 
small  black  seedless  grape,  is  the  same  as  for  seedless  raisins  except 
that  in  hot  climates  like  the  San  Joaquin  Valley  the  best  quality  is 
obtained  by  drying  in  the  stack  without  preliminary  exposure  to  direct 
sunshine. 

The  drying  of  dipped  or  bleached  grapes  in  a  dry-yard  is  similar 
to  that  of  untreated  grapes  in  the  vineyard.  In  drying  dipped,  but 
unsulfured  grapes,  the  bunches  should  be  turned  often  enough  to 
prevent  molding,  and  with  the  same  object,  the  trays  should  not  be 
stacked  until  the  raisins  are  too  dry  to  mold.  To  obtain  a  uniform 
light  amber  color  in  sulfur  bleached  raisins,  they  should  be  exposed 
to  direct  sunshine  as  short  a  time  as  possible — one  to  four  days,  accord- 
ing to  the  temperature.  After  the  grapes  have  acquired  a  uniform 
amber  color  and  are  partially  shriveled,  drying  is  preferably  completed 
in  the  stack. 

During  seasons  of  early  fall  rains,  considerable  delay  and  extra 
labor  is  unavoidable  in  completing  the  sun-drying  of  raisins.  Occa- 
sional light  showers  will  do  no  damage  if  the  trays  are  stacked  and 
covered  with  an  empty  tray  and  when  the  weather  clears,  the  trays 
are  spread  out  again.  Paper  trays  should  be  rolled  and  placed  under 
the  vines  for  protection  until  they  can  be  spread  out  again  to  complete 
drying.  Raisins  which  have  been  wet  by  rains  can  be  prevented  from 
molding  by  covering  each  stack  of  trays  with  a  sulfuring  hood  of 
suitable  size  and  shape  similar  to  that  shown  in  fig.  12,  and  burning 
about  half  a  pound  of  sulfur  to  each  25  trays  as  described  in  Circular 
211  of  this  station.  If  several  hoods  are  used,  the  operation  becomes 
rapid  and  continuous. 

If  a  long  period  of  rainy  weather  occurs,  recourse  must  be  had  to  a 
dehydrater.  While  dehydration  has  not  been  found  economical  in  the 
production  of  the  desired  quality  of  Muscat  raisins  starting  from  the 
freshly  picked  grapes,  the  use  of  dehydration  at  the  safe  temperature 
of  160°  F.,  is  valuable  in  rapidly  completing  the  drying  of  partially 
sun-dried  raisins  during  rainy  weather.  Growers  who  have  "rain 
damage"  dehydraters  for  emergency  use  have  been  able  to  save  the 
cost  of  such  dehydraters  in  a  few  years  because  of  the  greater  yield 
and  quality  of  raisins  obtained  by  delaying  the  picking  of  the  grapes 
until  they  have  reached  full  maturity.  Even  though  not  needed  every 
year,  an  inexpensive  dehydrater  is  valuable  as  insurance  against 
damage  or  loss  to  raisins. 

In  recent  years,  dehydraters  have  come  into  considerable  use  for 
drying  soda  dipped  or  sulfur  bleached  seedless  raisins  in  the  Sacra- 
mento Valley.     If  weather  permits,  the  trays  are  usually  spread  in 


Bull.  388]  PRINCIPLES    OF   SUN-DRYING    FRUIT  55 

the  dry-yard  for  one  day  to  give  the  raisins  a  more  uniform  color, 
after  which  drying  can  be  quickly,  and  economically  completed  in  the 
dehydrater.  For  safety,  the  temperature  should  not  exceed  160°  F., 
with  dipped,  or  150°  F.,  with  bleached  raisins. 


SUMMAEY  OF  COST  OF  DRYING 

During  the  survey  of  dry-yards,  on  which  the  information  presented 
in  this  bulletin  is  based,  much  valuable  information  on  the  costs  of 
picking  and  drying  fruits  was  obtained.  Although  not  a  primary 
function  of  this  bulletin,  it  was  thought  desirable  to  summarize  the  cost 
data  because  of  their  value  as  a  guide  in  estimating  costs  of  producing 
dried  fruits. 

As  few  growers  keep  itemized  accounts  of  their  costs  of  operation, 
it  was  necessary  to  calculate  average  costs  from  a  comparatively  small 
number  of  reports.  However,  all  the  data  used  in  compiling  the  follow- 
ing tabulations  were  obtained  from  exact  records  kept  by  experienced 
growers  and  may  be  considered  reliable. 

Some  of  the  more  important  factors  which  cause  variations  in  costs 
of  producing  dried  fruits  may  be  briefly  enumerated  as  follows : 

1.  Variety  of  fruit. 

2.  Size  of  fruit. 

3.  Acreage  yield. 

4.  Methods  of  picking,  cutting  and  drying. 

5.  Adequacy,  efficiency  and  arrangement  of  dry -yard  and  accessory 
equipment. 

6.  Rapidity  and  uniformity  of  drying  as  affected  by  climatic  and 
weather  conditions. 

7.  Rates  for  labor  and  supplies. 

8.  Efficiency  of  labor. 

9.  Drying  ratio  of  fruit. 

Because  of  these  variables,  some  of  which  are  beyond  the  control 
of  the  grower,  the  figures  given  in  the  following  tables  can  be  con- 
sidered only  as  approximate  averages. 

Growers  will  find  it  very  useful  to  keep  a  simple  account  book  in 
which  to  record  daily  the  quantity  of  green  and  dried  fruit  handled, 
itemized  costs  of  labor  and  supplies,  etc.  This  information  is  invaluable 
in  considering  economic  improvements  in  methods  or  equipment. 


56 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 


OPERATING  COSTS 

The  costs  given  in  the  following  tables  include,  in  addition  to  the 
labor  cost  of  picking,  all  items  of  labor  and  supplies  required  from  the 
time  the  fruit  is  delivered  to  the  dry-yard  until  the  dried  product  is  in 
temporary  storage  awaiting  shipment  to  a  packing  house.  There  are 
always  additional  charges  for  hauling  the  fresh  fruit  to  the  dry -yard 
and  for  hauling  the  dried  product  to  a  packing  house  which  are  not 
included  here  because  of  insufficient  data.  There  are  also  additional 
seasonal  charges  for  labor  in  washing,  repairing  and  storing  trays  and 
boxes;  in  care  of  dry -yard,  tracks  and  other  equipment  at  the  begin- 
ning and  end  of  the  season,  etc.,  which  must  be  prorated  among  the 
total  tons  of  fruit  dried  during  the  season.  Such  items  are  much  less 
than  the  direct  costs  of  handling  the  fruit  but  are  nevertheless  appre- 
ciable and  should  not  be  lost  sight  of  in  compiling  the  total  cost  of 
production. 

TABLE  12 

Average  Cost  or  Picking  and  Drying  Apricots  (Santa  Clara  County, 
Six  Growers,  1921) 


Per  dry  ton* 


Picking,  @  37^0  per  hour 

Cutting,  @  lie  per  40-lb.  box 

All  other  labor,  @  37^c  per  hour 
Sulfur,  7  lbs.  @  5c 

Totals 


$81.70 


Average  gross  shrinkage  5:1. 


TABLE  13 


Average  Cost  of  Picking  and  Drying  Peaches  (San  Joaquin  Valley, 
Four  Growers,  1921) 


Picking,  @  42^c  per  hour 

Cutting,  @  8c  per  50-lb.  box 

All  other  labor,  @  45c  per  hour 
Sulfur,  8^1bs.  @5c 

Total 


$11.32 


Per  green  ton 

Per  dry  ton* 

$3.02 

$15.10 

3.30 

16.50 

4.58 

22.90 

.42 

2.10 

$56.60 


Average  gross  shrinkage  5:1. 


Bull.  388] 


PRINCIPLES    OF    SUN-DRYING    FRUIT 


57 


Pears. — Table  14  summarizes  data  obtained  in  1921  at  several  large 
custom  dry-yards  in  Mendocino  and  Lake  counties  on  the  costs  of 
ripening,  cutting  and  drying  pears,  with  an  average  shrinkage  of  4.3  :1. 
The  cost  does  not  include  picking. 

TABLE  14 

Average  Cost  of  Drying  Pears 


Per  green  ton 


Per  dry  ton 


Cutting,  @  15c  per  box 

Labor  (all  other),  @  40c  per  hour 
Sulfur,  @,  4c  a  pound 

Total 


$5.10 
10.60 

.48 


$16.18 


$21.93 

45.58 

2.06 


$69.57 


Prunes. — The  figures  on  the  cost  of  picking  and  drying  prunes, 
presented  in  Table  15,  were  obtained  in  11  dry-yards  ranging  in  size 
from  small  to  large  and  equally  distributed  between  the  Santa  Clara 
and  Sacramento  valleys.  The  labor  and  supplies  required  for  dipping 
and  drying  ranged  from  $1.60  to  $6.15,  averaging  $4.21  a  green  ton. 


TABLE  15 
Average  Cost  of  Picking  and  Drying  Prunes   (1921) 


Per  dry  ton51 


Picking  (by  contract) 

Dipping,  Labor 

Supplies  (see  Table  9). 
Drying,  Labor  @  373^c  per  hour 

Total 


$20.51 


*  Average  shrinkage  2j:l. 

Figs. — Data  obtained  from  three  experienced  Calimyrna  fig 
growers  in  the  San  Joaquin  Valley  in  1921  showed  costs  of  $20  to  $22 
per  dry  ton  for  picking  and  drying,  of  which  $8  to  $10  per  ton  was 
paid  for  picking  at  the  rate  of  20  cents  for  each  40-  to  50-pound  box. 

Detailed  costs  of  drying  a  120-ton  crop  of  Adriatic  figs  is  presented 
in  Table  16. 

Limited  data  on  the  cost  of  picking  and  drying  Mission  figs  in  the 
orchard  by  the  sack  method  varied  from  $16  to  $20  per  dry  ton. 


58  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

TABLE  16 

Cost  of  Picking  and  Drying  Adriatic  Figs 
Kearney  Park  Vineyard — Fresno,  1921. 

Per  dry  ton 

Picking,  @  14c  per  46-lb.  box $8.16 

Labor,  dipping  and  drying,  @  40c  per  hour 13.07 

Salt,  19  lbs.  @  Mc 14 

Sulfur,  13  lbs.  @  4c 52 

Power,  14.5  K.W.H.  @  2^c.    (For  operation  of  dipper) 36 

Total $22.25 

Raisins. — Itemized  costs  of  all  the  operations  involved  in  raisin 
drying  were  not  obtained  but  records  obtained  in  1919  and  1920  from 
several  efficiently  operated  raisin  vineyards  in  the  San  Joaquin  Valley 
gave  costs  closely  approximating  $9  per  green  ton,  which,  on  an  average 
drying  ratio  of  3%  :1,  is  equivalent  to  $31.50  per  ton  of  finished  raisins. 
This  cost  includes  all  labor  and  teams  used  in  preparing  the  ground, 
distributing  trays  and  boxes  to  and  from  the  vineyard,  picking,  turn- 
ing, stacking  and  boxing,  but  not  hauling  to  the  packing  house.  Since 
that  time  the  cost  of  picking  and  traying  has  been  reduced  about  one- 
third  which  makes  present  costs  about  $7  per  green  ton  or  $24  per 
dry  ton.  An  additional  charge  of  1  cent  per  tray  and  5  cents  per 
sweat  box  should  be  allowed  for  annual  repairs. 

FIXED  CHAEGES 

Any  consideration  of  the  total  cost  of  drying  fruits  would  be 
incomplete  without  reference  to  the  annual  fixed  charges  on  the  equip- 
ment required.  Many  growers  neglect  to  include  this  important  item 
in  calculating  costs  of  production.  The  investment  in  each  of  the 
following  items  of  equipment  should  be  recorded. 

1.  Area  of  land  reserved  for  dry -yard. 

2.  Buildings  used  for  cutting,  dipping,  sulfuring  and  storing  fruits. 

3.  Lug  boxes,  trays  and  sweat  boxes. 

4.  Cars  and  tracks. 

5.  Accessory  equipment  such  as  dippers,  graders,  tables,  etc. 

In  general,  there  are  five  charges  properly  made  against  the 
investment  represented  by  this  equipment.  These  are  interest,  depre- 
ciation, upkeep,  insurance  and  taxes.  Interest  is  usually  calculated  at 
a  rate  of  5%  on  the  current  investment.     Depreciation  and  upkeep 


BULL.  3S8]  PRINCIPLES    OF   SUN-DRYING   FRUIT  59 

together  will  vary  from  5%  to  15%  according  to  the  nature  of  the 
equipment,  its  use  and  manner  of  construction.  For  instance,  dry-yard 
land  would  presumably  suffer  no  depreciation,  while  trays  and  boxes 
often  require  an  annual  depreciation  charge  of  10%  or  more.  Insur- 
ance on  combustible  buildings  and  equipment  is  frequently  carried  at 
rates  averaging  2%  to  3%  of  their  value.  Taxes  are  variable  but 
will  rarely  exceed  3%  on  an  assessed  valuation  equal  to  50%  of  the 
investment  (1%%  on  the  market  value). 

Taking  into"  consideration  the  entire  equipment,  including  land,  an 
annual  fixed  charge  of  about  15%  to  20%  is  usually  sufficient  to  cover 
all  the  above-mentioned  items.  However,  each  grower  should  care- 
fully determine  his  own  proper  allowance  for  fixed  charges.  This 
should  then  be  divided  by  the  number  of  tons  of  fruit  dried  during 
the  year  and  added  to  the  previously  recorded  direct  cost  of  labor  and 
materials  used  in  drying  the  fruit. 

Fixed  charges  per  ton  vary  rather  widely,  the  chief  factors  of 
difference  being :  first,  the  amount  and  nature  of  equipment  used  and, 
second,  the  tonnage  dried  in  any  given  year.  Sufficient  exact  data  on 
fixed  charges  from  which  to  compile  reliable  averages  was  not  obtained. 
However,  the  following  tables  are  presented  as  guides  in  tabulating 
equipment  costs  and  prorating  fixed  charges  thereon. 

Apricots. — The  investment  in  apricot  drying  equipment  given  in 
Table  17,  has  been  calculated  from  data  furnished  by  W.  R.  Kingston 
of  Ventura  County.  The  figures  are  for  equipment  capable  of  drying 
100  tons  (fresh  weight)  of  apricots  per  season.  Assuming  an  annual 
fixed  charge  of  15%  on  a  total  investment  of  $2253,  there  would  be  a 
fixed  charge  of  $3.38  per  fresh  ton,  which  on  a  drying  ratio  of  5  :1 
would  equal  $16.90  per  dry  ton.  No  charge  is  made  for  dry -yard  land, 
it  being  assumed  that  before  the  drying  season  some  annual  crop  of 
sufficient  value  can  be  harvested  from  the  land  to  at  least  cover  the 
interest  on  the  value  of  the  land  in  addition  to  the  cost  of  production. 

Similar  data  furnished  by  Martin  J.  Madison  of  the  California 
Prune  and  Apricot  Growers'  Association,  for  a  plant  capable  of  drying 
300  fresh  tons  of  apricots  per  season,  is  summarized  in  Table  18. 

Prunes.- — Data  obtained  from  four  prune  growers  in  Santa  Clara 
County  with  an  annual  production  of  70,  165,  190  and  1500  fresh  tons, 
respectively,  gave  fixed  charges  of  $3.64,  $2.60,  $4.24  and  $3.23  per 
fresh  ton,  respectively.  With  an  average  drying  ratio  of  21/4  :1,  the 
above  figures  represent  an  average  fixed  charge  of  $7.70  per  ton  of 
dried  prunes. 


60  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


TABLE  17 

Investment  in  Apricot  Drying  Equipment 
(After  W.  R.  Kingston,  Ventura  County) 

Cost  per 
Equipment  for  100  fresh  tons  per  season.  fresh  ton 

300—50  pound  picking  boxes  at  36c $1.08 

1200—3'  x  8'  trays  at  $1.05 12.60 

Cutting  shed,  1000  square  feet  area  at  20c 2.00 

Pitting  tables,  knives  and  pans 1.00 

8-tray  cars  at  $12.25 98 

1-transfer  car  at  $21.00 21 

475  feet  of  track  at  35c *. 1.66 

6  sulfur  houses  at  $25.00 1.50 

Storage  bin,  5'  x  15'  x  15'  at  $150.00 1.50 

Total  investment  per  fresh  ton $22.53 

Fixed  charge  per  fresh  ton  at  15% 3.38 

Fixed  charge  per  dry  ton  at  15% 16.90 


TABLE  18 

Investment  in  Apricot  Drying  Equipment 

(After  M.  J.  Madison,  San  ,)ose) 

Cost  per 
Equipment  for  300  fresh  tons  per  season.  fresh  ton 

1000—50  pound  picking  boxes  at  253^c $     .85 

6000—3'  x  8'  trays  at  70c 14.00 

Cutting  shed,  36'  x  94' 2. 58 

Pitting  tables,  knives  and  pans 33 

17  tray  cars  at  $10.00 57 

2  transfer  cars  at  $12.50 08 

2  turntables  at  $12.50 08 

1500  feet  of  track  with  rails,  ties  and  spikes 78 

15  sulfur  houses  at  $33.00 1. 65 

Warehouse— 36' x  60' 4.00 

7  hand  trucks  and  1  platform  scale 77 

Total  investment  per  fresh  ton $25.69 

Fixed  charge  per  fresh  ton  at  15% 3.85 

Fixed  charge  per  dry  ton  at  15% 19.25 


STATION  PUBLICATIONS  AVAILABLE  FOR  FREE  DISTRIBUTION 


BULLETINS 

No.  No. 

253.  Irrigation  and   Soil  Conditions  in  the  352. 
Sierra  Nevada  Foothills,  California. 

261.  Melaxuma    of    the    Walnut,    "Juglans  353. 

regia."  354. 

262.  Citrus  Diseases   of  Florida  and  Cuba  357. 

Compared  with  Those  of  California. 

263.  Size  Grades  for  Ripe  Olives. 

268.   Growing  and  Grafting  Olive  Seedlings.  358. 
273.   Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain.  359. 

275.  The  Cultivation  of  Belladonna  in  Cali-  361. 

fornia. 

276.  The  Pomegranate.  362. 

277.  Sudan  Grass  363. 

278.  Grain  Sorghums. 

279.  Irrigation  of  Rice  in  California.  364. 

280.  Irrigation  of  Alfalfa  in  the  Sacramento 

Valley.  366. 

283.  The  Olive  Insects  of  California. 

285.  The  Milk  Goat  in  California.  367. 

286.  Commercial  Fertilizers. 

294.  Bean  Culture  in  California.  368. 
304.  A  Study  of  the  Effects  of  Freezes  on 

Citrus  in  California.  369. 

310.  Plum  Pollination.  370. 

312.  Mariout  Barley.  371. 

313.  Pruning  Young  Deciduous  Fruit  Trees. 

319.   Caprifigs  and  Caprification.  372. 

324.  Storage  of  Perishable  Fruit  at  Freezing 

Temperatures.  374. 

325.  Rice  Irrigation  Measurements  and  Ex- 

periments    in     Sacramento     Valley, 
1914-1919.  375. 

328.  Prune  Growing  in  California. 

331.  Phylloxera-Resistant  Stocks.  376. 

334.  Preliminary  Volume  Tables  for  Second- 

Growth  Redwood.  377. 

335.  Cocoanut   Meal   as   a   Feed   for  Dairy  379. 

Cows  and  Other  Livestock.  380. 

339.  The  Relative  Cost  of  Making  Logs  from 

Small  and  Large  Timber.  381. 

340.  Control  of  the  Pocket  Gopher  in  Cali- 

fornia. 382. 

343.  Cheese  Pests  and  Their  Control. 

344.  Cold  Storage  as  an  Aid  to  the  Market-  383. 

ing  of  Plums. 

346.  Almond  Pollination.  384. 

347.  The  Control  of  Red  Spiders  in  Decidu- 

ous Orchards. 

348.  Pruning  Young  Olive  Trees.  385. 

349.  A    Study    of    Sidedraft    and    Tractor  386. 

Hitches. 

350.  Agriculture  in  Cut-over  Redwood  Lands.  387. 


Further  Experiments  in  Plum  Pollina- 
tion. 

Bovine  Infectious  Abortion. 

Results  of  Rice  Experiments  in  1922. 

A  Self-mixing  Dusting  Machine  for 
Applying  Dry  Insecticides  and 
Fungicides. 

Black  Measles,  Water  Berries,  and 
Related  Vine  Troubles. 

Fruit  Beverage  Investigations. 

Preliminary  Yield  Tables  for  Second 
Growth  Redwood. 

Dust  and  the  Tractor  Engine. 

The  Pruning  of  Citrus  Trees  in  Cali- 
fornia. 

Fungicidal  Dusts  for  the  Control  of 
Bunt. 

Turkish  Tobacco  Culture,  Curing  and 
Marketing. 

Methods  of  Harvesting  and  Irrigation 
in  Relation  to  Mouldy  Walnuts. 

Bacterial  Decomposition  of  Olives  dur- 
ing Pickling. 

Comparison  of  Woods  for  Butter  Boxes. 

Browning  of  Yellow  Newtown  Apples. 

The  Relative  Cost  of  Yarding  Small 
and  Large  Timber. 

The  Cost  of  Producing  Market  Milk  and 
Butterfat  on  246  California  Dairies. 

A  Survey  of  Orchard  Practices  in  the 
Citrus  Industry  of  Southern  Cali- 
fornia. 

Results  of  Rice  Experiments  at  Cor- 
tena,   1923. 

Sun-Drying  and  Dehydration  of  Wal- 
nuts. 

The  Cold  Storage  of  Pears. 

Walnut  Culture  in  California. 

Growth  of  Eucalyptus  in  California 
Plantations. 

Growing  and  Handling  Asparagus 
Crowns. 

Pumping  for  Drainage  in  the  San 
Joaquin  Valley,   California. 

Monilia  Blossom  Blight  (Brown  Rot) 
of  Apricot. 

A  Study  of  the  Relative  Values  of  Cer- 
tain Succulent  Feeds  and  Alfalfa  Meal 
as  Sourses  of  Vitamin  A  for  Poultry. 

Pollination  of  the  Sweet  Cherry. 

Pruning  Bearing  Deciduous  Fruit 
Trees. 

Fig  Smut. 


CIRCULARS 


No. 

87.  Alfalfa. 
113.   Correspondence  Courses  in  Agriculture. 
117.  The    Selection    and    Cost    of    a    Small 

Pumping  Plant. 
127.  House  Fumigation. 
129.  The  Control  of  Citrus  Insects. 
136.  Melilotus    indica    as    a    Green-Manure 

Crop  for  California. 
144.    Oidium  or  Powdery  Mildew  of  the  Vine. 

151.  Feeding  and  Management  of  Hogs. 

152.  Some  Observations  on  the  Bulk  Hand- 

ling of  Grain  in  California. 
154.   Irrigation   Practice   in   Growing   Small 
Fruit  in  California. 


No. 

155.   Bovine  Tuberculosis. 

157.   Control  of  the  Pear  Scab. 

160.  Lettuce  Growing  in  California. 

161.  Potatoes  in  California. 

164.  Small  Fruit  Culture  in  California. 

165.  Fundamentals   of   Sugar   Beet  Culture 

under  California  Conditions. 

166.  The  County  Farm  Bureau. 

167.  Feeding  Stuffs  of  Minor  Importance. 
170.  Fertilizing  California  Soils  for  the  1918 

Crop. 
173.  The    Construction    of    the    Wood-Hoop 

Silo. 
178.  The  Packing  of  Apples  in  California. 


CIRCULARS — {Continued) 


No. 
179. 

184. 
190. 
199. 
202. 

203. 
208. 

209. 
210. 
212. 
214. 

215. 
217. 

220. 
228. 
231. 
232. 

233. 
234. 

235. 

236. 

237. 

238. 
239. 

240. 

241. 


244. 
245. 
247. 
248. 

249. 
250. 


Factors    of    Importance    in    Producing 

Milk  of  Low  Bacterial  Count. 
A  Flock  of  Sheep  on  the  Farm. 
Agriculture  Clubs  in  California. 
Onion  Growing  in  California. 
County   Organizations   for  Rural   Fire 

Control. 
Peat  as  a  Manure  Substitute. 
Summary  of  the  Annual  Reports  of  the 

Farm  Advisors  of  California. 
The  Function  of  the  Farm  Bureau. 
Suggestions  to  the  Settler  in  California. 
Salvaging  Rain-Damaged  Prunes. 
Seed  Treatment  for  the  Prevention  of 

Cereal  Smuts. 
Feeding  Dairy  Cows  in  California. 
Methods   for  Marketing  Vegetables   in 

California. 
Unfermented  Fruit  Juices. 
Vineyard  Irrigation  in  Arid  Climates. 
The  Home  Vineyard. 
Harvesting    and    Handling    California 

Cherries  for  Eastern  Shipment. 
Artificial  Incubation. 
Winter  Injury  to  Young  Walnut  Trees 

during  1921-22. 
Soil  Analysis  and  Soil  and  Plant  Inter- 
relations. 

The  Common  Hawks  and  Owls  of  Cali- 
fornia   from    the    Standpoint   of   the 

Rancher. 
Directions  for  the  Tanning  and  Dress- 

of  Furs. 
The  Apricot  in  California. 
Harvesting  and  Handling  Apricots  and 

Plums  for  Eastern  Shipment. 
Harvesting    and    Handling    Pears   for 

Eastern  Shipment. 
Harvesting  and  Handling  Peaches  for 

Eastern  Shipment. 
Marmalade  Juice  and  Jelly  Juice  from 

Citrus  Fruits. 
Central  Wire  Bracing  for  Fruit  Trees. 
Vine  Pruning  Systems. 
Colonization  and  Rural  Development. 
Some  Common  Errors  in  Vine  Pruning 

and  Their  Remedies. 
Replacing  Missing  Vines. 
Measurement  of   Irrigation   Water   on 

the  Farm. 


No. 

251.  Recommendations  Concerning  the  Com- 

mon    Diseases     and     Parasites     of 
Poultry  in  California. 

252.  Supports  for  Vines. 

253.  Vineyard  Plans. 

254.  The  Use  of  Artificial  Light  to  Increase 

Winter  Egg  Production. 

255.  Leguminous  Plants  as  Organic  Fertil- 

izer in  California  Agriculture. 

256.  The  Control  of  Wild  Morning  Glory. 

257.  The  Small-Seeded  Horse  Bean. 

258.  Thinning  Deciduous  Fruits. 

259.  Pear  By-products. 

260.  A  Selected  List  of  References  Relating 

to  Irrigation  in  California. 

261.  Sewing  Grain   Sacks. 

262.  Cabbage  Growing  in  California. 

263.  Tomato  Production  in  California. 

264.  Preliminary  Essentials  to  Bovine  Tuber- 

culosis Control. 

265.  Plant  Disease  and  Pest  Control. 

266.  Analyzing  the  Citrus  Orchard  by  Means 

of  Simple  Tree  Records. 

267.  The  Tendency  of  Tractors  to  Rise  in 

Front;  Causes  and  Remedies. 

268.  Inexpensive  Lavor-saving  Poultry  Ap- 

pliances. 

269.  An  Orchard  Brush  Burner. 

270.  A  Farm  Septic  Tank. 

271.  Brooding  Chicks  Artificially. 

272.  California  Farm  Tenancy  and  Methods 

of  Leasing. 

273.  Saving  the  Gophered  Citrus  Tree. 

275.  Marketable       California        Decorative 

Greens. 

276.  Home  Canning. 

277.  Head,   Cane,   and  Cordon  Pruning  of 

Vines. 

278.  Olive  Pickling  in  Mediterranean  Coun- 

tries. 

279.  The  Preparation  and  Refining  of  Olive 

Oil  in  Southern  Europe. 

281.  The  Results  of  a  Survey  to  Determine 

the  Cost  of  Producing  Beef  in  Cali- 
fornia. 

282.  Prevention  of  Insect  Attack  on  Stored 

Grain. 

283.  Fertilizing  Citrus  Trees  in  California. 

284.  The  Almond  in  California. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 


20m-6,'25 


